look up any word, like half chub:
 
4.
Failing to be cool. Trying to be cool and being just pathetic.
-John: Hey, girls! Look at my new trainers! I think they're great!
-Kate (to her friends): This guy is just not cool.
by sicko2 March 02, 2008
 
1.
An expression on how something is... well, not cool. Very similar to the following expression: gay, retarded, lame, etc.
"Dude, you got drunk and danced naked in the middle of the freeway while singing "Jingle Bells" in Spanish?!"

"Dude, I know. Totally not cool."
_ _ _ _

Not cool situation: When you get an "F" on your math test because you studied the wrong chapter... three minutes prior to the test ^_^
_ _ _ _

*Bitch slap* <---- Not cool.
_ _ _ _

Boyfriend: "I have something to tell you..."
Girlfriend: "You love me? =)"
Boyfriend: "Uh, I'm gay."
Girlfriend: "What? NOT AGAIN! This is SO not cool"
by Psych! November 27, 2005
 
2.
When someone has done something which causes you anger and displeasure. You respond by throwing down any item which you are currently holding and yell: "NOT COOL!". Of great importance: the item which has been throw down is now considered community property and may be taken by anyone witnessing said event.
Cool Guy: (walking into a room of friends/coworkers eating burritos) Dude, where's my burrito?
Not Cool Guy: I think they forgot to make it. Or maybe I forgot to order it. (smirks)
Cool Guy: (throwing down container of guacamole -- which he intends those in the room to now eat) NOT COOL!
by not cool guy eating a burrito January 14, 2014
 
3.
Just plain lame
That shit just is not cool, man. Why'd you desert your homies at a time of need?
by Anon255 February 13, 2013
 
5.
The ultimate phrase to describe those who are at times 'lame' as the terminology an American would maybe use.
"James is NOT COOL!"
by DarkestMaiden March 09, 2007