"That guy" refers to the narcissist inside each and every man. "He" is "That guy" when he gives into the urges (usually pertaining to sexual gratification) to the detriment of those around him. Nobody wants to be "That guy".
Bob: "Dude... don't freak... I got a blowjob from your sister last night ... but I don't want to be 'That guy'".

Another Bob: "Look at 'That guy' next to 'prince cassius' in the fashion section of the evening standard".
by jeffreythefarmer2 August 17, 2010
"That Guy" is the guy that you know of, but do not know personally. You see him at the bowling alley every week and he is just the sliest old man you've ever met. That guy has bowled 300's on several occasion which makes you want to know him even more. He's an asshole and as much as you want to hate him you cant, because he's THAT GUY. Just when you think you've had enough of THAT GUY, he openly makes fun of a person you dislike and he draws you in even further.
Morgan Freeman: "Look, someone is about to bowl another 300 game!"
Edward Scissorhands: "It's THAT GUY! Man, I hate him"
Morgan Freeman: "No you don't"
Edward Scissorhands: "You're right, I love THAT GUY"
by Moe0618 October 9, 2012
A mysterious figure, often someone with mad skills. Every sport has a That Guy as does every branch of the Military. That Guy is often the topic of conversation among aspirants in these fields. Such as High School football players referring to That Guy on an NFL team or Soldiers referring to That Guy on the Special Forces Detachment.
Soldier 1: That Urban training was rough, beat my old best time though.

Soldier 2: Yeah me too, but That Guy smoked us.

Soldier 1: Yeah, who was That Guy?

Are you That Guy?
by Corpy007 April 27, 2010
The player that got you... and your friends.. and everyone.. but you still like him secretly.
That guy kissed me yesterday! But then when I got home I found out he was goin out with the new girl.
by mezougel December 11, 2010
The awkward guy nobody knows who inexplicably makes weird faces in the background of every picture.
Girl: Look how cute our prom pictures are!
Boyfriend: Yeah, except for That Guy.
by skittlesbunnyx3 July 11, 2008
That guy, is the person who enters an online video game just to mess with people. The "That Guy" is in every game room. He/She can range from someone who just messes around killing his teammates or someone with just a high pitch voice.
That Guy: Oops I killed my whole team again.
You: Oh great its That Guy.

Kid with high pitch voice: Hey guys are you ready for fun?!
You: We have officially found That Guy.
by Todd Feipel May 14, 2008
That guy, is the person who enters an online video game just to mess with people. The "That Guy" is in every game room. He/She can range from someone who just messes around killing his teammates or someone with just a high pitch voice.
That Guy: Oops I killed my whole team again.
You: Oh great its That Guy.

Kid with high pitch voice: Hey guys are you ready for fun?!
You: We have officially found That Guy.
by Todd Feipel May 14, 2008