a male that acts in a certain fashion in a given situation, fully knowing such act is considered rude, obscene, or otherwise frowned upon in normal social interaction.
Didn't he just hit on the girl he knows you are dating? Yeah, he's "that guy".
Hey, can i bum your last cigarette? It's my last one, don't be "that guy".
“I nominate That Guy!”
Theotherguy- "Yeah, especially when he kept screaming then telling people to shut up."