Depending on the context can be a way to point some out. Or used as a durogative. Or as a method of surprise
1. A phrase used to point out a guy in the room.
2. Used in conjunction with the word "oh" can be used as a durogative. A durogative meaning "oh God not him" or "Look guys, it's the guy we dislike, hate, find creep, we blame, find annoying, etc. Kinda like "oh" in the movie h@me.
3.a character in futurama.
"Oh that guy" said the crowd who were rolling there eyes as there "friend" approached .
Someone who talks too much and you want them to just shut up for once. This can apply to not just girls, but boys too.
Brian: Yo, that guy talks too much. Can't he just shut up already?
Joe: I dunno man, it seems like he just can't stop.
Why are you even reading this, you know your not that guy.
Look at jimmy over there, he’s not that guy.
A person who is not important enough for anyone to remember their name. That guy is most likely a loner or socially awkward.
Who the hell is that guy and why should I even care?
That guy is a nickname for someone who is generally annoying and always sort of a dick.
Person 1: Wait, is that..?
Person 2: Ugh, it's THAT guy.