I'm looking for an idiom or expression for describing people who tell lies out of habit (so you cannot trust them at all).
I know that these people are called "compulsive liars", but I'm not looking for psychological terms.
Is there any idiom or expression for describing such people?
For example:
"Did X tell that to you?! Come on, don't believe him/her. Don't you know he/she ___ (=is a habitual liar)?"
I've often heard "lies like a rug"
From McGraw-Hill Dictionary of American Idioms and Phrasal Verbs:
to tell lies shamelessly. He says he didn't take the money, but he's lying like a rug. I don't believe her. She lies like a rug
I would use "pathological liar" which is broadly used to describe someone who habitually lies. The Wikipedia article on Pathological lying explains:
Pathological lying (also called pseudologia fantastica and mythomania) is a behavior of habitual or compulsive lying. It was first described in the medical literature in 1891 by Anton Delbrueck. Although it is a controversial topic, pathological lying has been defined as "falsification entirely disproportionate to any discernible end in view, may be extensive and very complicated, and may manifest over a period of years or even a lifetime". The individual may be aware they are lying, or may believe they are telling the truth. Sometimes however, the individual may be lying to make their life seem more exciting when in reality they believe their life is unpleasant or boring.
I heard this term used very often. Dictionary.com has the following definition:
a person who tells lies frequently, with no rational motive for doing so.
Sounds like the person in question is full of shit!
This doesn't necessarily imply the lying is habitual, although you can modify it rather easily with any word indicating frequency:
Yea I know Bob said that, but Bob is usually full of shit.
Or just use it as is:
Bob said that? He's full of shit.
You can use "full of it" to avoid using "shit" in more polite contexts.
Other more polite forms include full of crap, full of bull, or full of baloney (thanks @DamianYerrick).
"She lies like she breathes" would be the common idiom that comes to mind for me.
Interestingly, I can't find any references online that directly discuss or define this idiom, but it is common as an American idiom, implying that lying is as easy and essential to a given person as breathing, with the additional insinuation that (like breathing) they just lie all the time.
Googling the phrase produces a number of book, article headlines ('The Man Who Lies Like He Breathes Calls President Obama’s Campaign “Disgraceful”', http://www.politicalgarbagechute.com/the-man-who-lies-like-he-breathes-calls-president-obamas-campaign-disgraceful/), and excerpts from comment sections where this phrase is used.
I did see an alternate, "you can tell he's lying because he's breathing," but that seems more unwieldy and more literal.
Not specific to lying, but I'm fond of the word inveterate:
Having a particular habit, activity, or interest that is long-established and unlikely to change
So inveterate liar does genuinely mean someone who lies out of habit.
Two common similes suggested by "Similes from the Folk Speech of the South: A Supplement to Wilstach" in Southern Folklore Quarterly, volume 4 (1940) are "X lies like a dog" and "X lies like a rug." I have heard both of those expressions many times, in the U.S. South and elsewhere.
Frank Wilstach, A Dictionary of Similes (1917) has some lively examples that are considerably less common. My favorite is this anonymous one:
Lies as fast as a dog can lick a plate.
Evidently this expression goes back to the 1500s at least. John Heywood, A Dialogue of the Effectual Proverbs in the English Tongue Concerning Marriage (not later than 1562) gives the saying as
She will lie as fast as a dog will lick a dish.
A common way to describe such a person in the UK is "Billy Bullshit[ter]".
Don't listen to Dave, he's a right Billy Bullshitter.
Habitual/chronic liar are more colloquial definitions used to refer someone who is in the habit of lying.
Ngram: habitual liar, chronic liar.
Like the song by Megan Trainor says, "I know you lie, [be]cause your lips are moving"... Personally I like the term "pathological liar" - I have known several people who fit the description. They actually believe their own lies. Other terms are "storytellers", "Web weavers", "spinners" (weaving a "Web of lies"),"habitual liar"... A common expression referring to a "chronic liar" is to "divide by 2" as in "Whatever he tells you, divide by 2"
This is a little lengthy, but "He'd rather climb a tree and tell a lie than stand on the ground and tell the truth." It rolls off the tongue better than it reads.
Crooked as a barrel of fish hooks or crooked as a dog's hind leg, from TFD
very dishonest.
"Don't play cards with him. He's as crooked as a barrel of fish hooks."
"Mary says all politicians are crooked as a dog's hind leg."
Barefaced liar, from TFD
One who tells blatantly obvious and/or impudent untruths easily and with little or no attempt to disguise the lie.
"Everyone knows he is just a barefaced liar. It's a wonder anyone believes a thing he says anymore."
Lie through teeth, from TFD
Fig. to lie boldly.
"I knew she was lying through her teeth, but I didn't want to say so just then."
"If John denies it he's lying through his teeth, because I saw him do it."
"Don't you know she lies through her teeth?"
If the person has been telling lies all their life, try:
Live a lie, from TFD
to live a life that is dishonest because you are pretending to be something that you are not, either to yourself or to other people.
"Walker, who admitted that he was gay last year, spoke of the relief he felt at no longer having to live a lie."
"For all of his adult life, he lived a lie and didn't confess even to his family that he was a spy."
I have heard it in casual conversation cleverly expressed in this way:
How do you know X is lying? He is moving his mouth.
Meaning anything that comes out of X's mouth is a lie.
To use your example as context:
Did X tell that to you!? Come on, don't believe him. How do you know X is lying? He is moving his mouth.
"persistently economical with the truth."
Here are a few favourites I have heard, "I cannot say he/she is lying, but I believe he/she is stranger to the truth."
"Just because it's brown, doesn't make it chocolate."
"Just because she feeds it to me doesn't mean I have to swallow."
As others have suggested, "Pathological liar" is a familiar idiom. If you want to suggest in an offhand way the person is generally unreliable or otherwise untrustworthy, use something like "I wouldn't trust him as far as I could throw him." It's a little folksy and paints a humorous analogy.
For someone who lies habitually, for professional reasons, but who is quite capable of telling the truth in his private life, I would use "snake oil salesman."
For someone who habitually lies in public or in private but who can, albeit with some effort and psychological discomfort, tell the truth when it is in his interests to do so, I would use "politician."
For someone who is incapable of telling the truth on any occasion, public or private, even when it is against his interests to lie, I would use "reporter."
Such a person can be called a Munchausen, who was a famous liar, and even gave name to a syndrome, although that is more specific (as in, lying about having a disease). I cannot provide any data on the usage except for the anecdotal "I've heard people use it", though.
Say he's a Pinocchio. From the story of Pinocchio, a puppet whose nose grew longer everytime he lied.
You could use "boy who cried wolf", which from the folk story of that name implies someone who lies so much that nobody can believe them even when they're telling the truth. Even using just part of the phrase is enough, e.g.: "I suspect (s)he's just crying wolf again".
The expression you're seeking is "Clintonian", named for the man who told us that the truth depended on what your definition of "is" is. According to an Arkansas official who knew him well, "Bill Clinton would rather climb a tree to tell a lie than stand on the ground to tell the truth."
If you're looking for somewhat more understated phrases, you can say that someone is "not known as a reliable source".
I like Judge Milian's expression she uses in the TV show, The People's Court:
I wouldn't trust what you said if your tongue came notarized.
He's "Pissing in your pocket, while telling you it's raining", if you're after a humorous expression.
Another expression I've heard is being "loose with the truth", though a similar expression was mentioned in the comments before.
One other would be that he's "Speaking/Talking out of his arse" (i.e. speaking shit).
"He couldn't lie straight in bed."
This seems to be a mainly Australian/NZ term. e.g. Here, here.
It's interesting because superficially it seems to be saying someone can't lie very well, but in reality it's pointing out how crooked they are.
This might or mightn't work, depending on your context, but if it's for someone who has a habit of embellishing their stories, you could say "take it with a pinch of salt":
Did X tell that to you?!
Come on, don't believe him.
Don't you know you have to take what he says with a pinch of salt?
From Collins:
With a pinch of salt or
with a grain of salt
without wholly believing; sceptically
While it covers more than just lying, "snake in the grass" seems to fit the bill. This is often shortened to just "snake" (definition two).
Probably not an exactly fit, but how about truth bender from the idiom bend the truth
e.g.
Politicians are such a truth benders
