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 28, 2005
Get the Not cool mug.
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
Get the Not cool mug.
laid back, relaxed, not freaked out, knows what's goin on.

has come to mean anything popular
"that's one cool cat."

"wow, that good charlotte (cough*sucks*cough) cd is cool!"
by ophelia November 29, 2003
Get the cool mug.
Showing approval. Something that is favored.
Hey I just got a new ______.
Coolness.
by El Fredo April 11, 2004
Get the Coolness mug.
An adjective referring to something that is very good, stylish, or otherwise positive. It is among the most common slang terms used in today's world.
by Ainolketta February 20, 2005
Get the cool mug.