Something like "latecomer" but for departing rather than arriving.
For example, "Bob was always the _____ at social outings."
Other variations with verbs or non - noun idioms are useful to me as well, such as "Bob would always ________ at social outings."
Guests who stay too long can be said to overstay their welcome or wear out their welcome. That is, their host grows tired of their presence and wishes they would leave.
The idiom is not limited to "staying too late," and also applies to other sorts of unwelcome behavior:
To behave in an offensive, burdensome, or tiresome manner, with the result that one's continued presence is unwanted within a residence, commercial establishment, or social group. (WT)
The overstay variant, though sometimes considered synonymous with the wear out version, more strongly emphasizes the length of the visit. It is more commonly used in British English (ngram), while wear out is more popular in American English (ngram).
The verb overstay by itself also communicates the act of staying too long, but less idiomatically (WT). If you require a noun, some derive overstayer (WT) from the verb, as used in a LifeHacker article:
People won't always get your subtle hints. Sometimes you need to tell an overstayer directly that the conversation and hang out time is over.
outstay more idiomatic than overstay ...ngram link is too long to post in a comment but seems to confirm
Commented
Oct 27, 2015 at 16:55
The word "straggler" comes to mind, meaning "a person or an animal that is among the last or the slowest in a group to do something, for example, to finish a race or leave a place."
‘The majority have returned to breeding grounds by late March, but stragglers have lingered locally until the end of May.’
‘The library was nearly deserted except for a few stragglers checking out books or reading in corners.’
‘No, the last stragglers, the tourists and the visitors, have now left the palace.’
It may be a bit slang, but I immediately thought of the word lingerer, as used in Pineapple Express:
https://www.youtube.com/watch?v=0sN0K1NS6b8
F***in' lingerer, man.
(Said after kicking someone out of his apartment).
laggard
: someone who takes more time than necessary; someone who lags behind Princeton University Wordnet
dawdler
dawdle: to take more time than necessary: dawdled through breakfast. The American Heritage® Dictionary
"Bob was always the laggard at parties, dawdling around and leaving after everyone else"
I would refer to such a person as a hanger-on.
My particular idiom comes from Glasgow in Scotland. I wouldn't regard this expression as particularly regional, however, and would expect it to be understood throughout the UK or even beyond.
I'll offer "last man standing" - the connotation of being able to carry on partying when everyone else has run out of steam.
In particular the connotations of the victor in some endurance feat. This doesn't convey the same 'outstaying welcome' connotations as some of the other answer.
He'll stay till the last dog is hung.
"When anybody from around here wanted to say they were still present at the end of a big party, they would say they had 'stayed until the last dog was hung.' Most of them probably had no idea anymore that they were talking about the Seneca New Year's celebration in the winter, where on the fifth day they used to strangle a white dog and hang it on a pole, Nobody had done that for at least a hundred years." --- Dance for the Dead, by Thomas Perry (Random House, New York, 1996)
Surprisingly, no one has suggested this aphorism attributed to Benjamin Franklin in 1736
Guests, like fish, begin to smell after three days.
In the 16th century, guests who seemingly had taken permanent residence were compared to three-day-old fish. The following quote is by John Lyly (1554-1606)
Fish and guests in three days are stale.
Source: Dictionary of Proverbs
My father once told the joke about how to get guests who have worn out their welcome to leave: "Wife, let's go to bed so our guests can go home."
Consider the expression "closing time":
the time at which pubs must legally stop selling alcoholic drinks
(http://www.thefreedictionary.com/closing+time)
By extension, this also means the very end of a social gathering.
So you could say something like: "Bob would never leave a party before closing time".
This may not be pertinent to parties, but night owl is a term which is generally used to refer anyone who stays up late at night.
The 'thing that wouldn't leave' has always been my favorite
"party killer", as coined by the NYC band Mongrel Bitch: "I'm a party killer and I'm not going home, as long as there"s beer you'll never be alone"...
