You're driving and get stuck in the middle of the intersection just as the light turns red. Now, because of you no one can get by. You have now become "That Guy".
The most annoying person at a social outing or gathering, especially when alcohol is involved.
Whatshisnuts- "Dude, So-and-so was being 'That Guy' at the party last night."
Theotherguy- "Yeah, especially when he kept screaming then telling people to shut up."
An individual at any given social event who crosses the line of severe Obscenity/Indecency/Profanity typically involving speech or actions, often vulgar and unnecessary. Doing so defines his title of "That guy". See also; jackass, Andrew, Fatkid.
Party Goer "Yes I do indeed enjoy box wine."
That Guy "I go down on my fat ex girlfriend when its her time of the month"
Party Goer" Oh, so you're that guy, please get away from me"
That Guy " Waaaahhhh You think I'm a fat loser and I only like fat chicks."