"Selfish" could mean anything from taking the last cookie to killing someone for the last cookie. Is there a harsher word for selfish that emphasises that it's wrong and/or hurtful?
Synonyms like "egoistic", "egocentric", "self-centered" "self-loving", etc, are no stronger than selfish. I would use an adverb before "selfish" lest its exact meaning be changed. "Egocentric" and "self-centered" are not exactly the same as selfish.
He is extremely/incredibly/profoundly/exceptionally/monstrously/etc selfish.
overly concerned with one's own desires, needs, or interests
- a brilliant but egomaniacal urban planner who ruthlessly sought to impose his vision of the ideal cityscape (M-W)
Avaricious denotes a kind of selfishness that knows no limits.
From the link:
avaricious | adjective | av·a·ri·cious | \ˌa-və-ˈri-shəs\
- greedy of gain; excessively acquisitive especially in seeking to hoard riches
an avaricious scheme to con the elderly couple out of thousands of dollars
I respectfully disagree that an adverb is the ideal route. English is the richest lexicon that has ever existed: you have an arsenal of words from which to choose the ideal way to fillet your subject.
Your question is short, but you asked for a word that conveys two meanings: selfishness, and that the selfishness is "wrong." I will interpret that as morally wrong.
- We say people are inconsiderate when they are selfish in a situation when it is wrong to be selfish.
- Self-seeking and self-serving both connote selfishness that is wrong.
- In specific situations, such as the case of the cookie caper, narrower words are fantastic: gluttonous and greedy are so wrong that Christians list them as two of the seven worst sins.
- Stingy and parsimonious are clearly wrong, but the selfish aspect is not as strongly present as some of the other words.
Which do you feel has more punch?
He ate all of the cookies again. He is extremely selfish.
All the cookies are gone. That gluttonous pig.
Whether you want a broad word or a narrow term, there is almost certainly something more provocative than "extremely."
If you're really looking for a word that means "would kill for a cookie", then I think you need something a bit stronger than what I see suggested so far. Suggestions include: psychopathic, psychotic, psycho, homicidal, maniac, murderous, deranged, unhinged, demented, narcissistic, megalomaniacal.
The term stingy has a fairly negative connotation
Unwilling to give or spend; ungenerous:
his employer is stingy and idle
he was stingy with his information
Oxford Dictionaries Online
The term niggardly is very pejorative
grudgingly mean about spending or granting: begrudging
However it is rarely used, most likely because it is so similar sounding to a racial epithet. See this usage note from Oxford Dictionaries Online
The words niggard and niggardly have no connection with the highly offensive term nigger, but because of the similarity of sound and its negative meaning of ‘mean, ungenerous,’ many people are uncomfortable with using it for fear of causing offense, and in the US it is now widely avoided.