Top definition
adj.
Someone who thinks that they are cool and/or smart but really isn't.

Or

Someone who is dumb,annoying or lame.
Example 1

Dude 1: Two plus two is four!

Dude 2: Wow, you are such a jackace!

Example 2

Guy 1: That was awesome! (After doing a stunt badly, not realizing it)

Guy 2: Shut up jackace! You did it all wrong!

Guy 1: No I didn't!
by Word Corrector September 16, 2009
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