The one person who nobody likes and just has to ruin everyone's fun. Commonly seen being a douchebag while committing actions that are completely irrelevant to the situation.
Josh: Guys, I just found out I actually like football. I might keep playing if no stupid jackasses show up this time.
Doug: Oh God, here comes that guy.
That Guy: Sup guys. Any of you get laid yet? Josh, are you still a virgin? I'm gonna get you laid this summer.
Josh: That's it, I'm gone.
That Guy: Hold on, guys, I'm gonna fire up some mary-j for a minute. *starts puffing away on a joint*
by Implying713 June 24, 2011
At any social gathering, someone who can not handle thier booze, needs to be escorted out of the situation, possibly by force
Mike: did you see that guys get pepper sprayed, tased and ruffed up
Jimmy: Yeah that guy was loaded.
by MikeGol August 22, 2008
You know him. He's That Guy, you know That Guy when you see him. He's straight BALLEN when my man walks in a crowd of people, they all stop.
I'm That Guy you will never be That Guy
Back in my day, I was That Guy. I got all the woman
by JTX_4777$ January 17, 2023
That guy is the guy who does things for the girl hes with or the girl he likes in gratitude of her actions with him.
Cam: I want a massage.

Micki: I will give you a massage.
Cam: I will give you one back, I'm just That Guy.
by JesusCam August 12, 2014
This is the guy that Chick Fil A serves on Sundays, told Katy Perry she’s just a plastic bag, and this guy probably 69s while being on top. If you see “that guy” you’re best move is probably just letting him cut you in line and hoping he remembers you one day.
Guy #1: “I heard Kim Jong-un doesn’t poop

Guy #2: “Nah, you’re mixing him up with That Guy”
by Zippity Zapped April 6, 2021
That guy is one who attends a party only to take advantage someone's drunk girlfriend. Now not only did you ruin her life, but you also pissed off her boyfriend likewise all for your own greed. Perhaps this can be a tactic for vengeance, perhaps you are just a douchebag. Whatever the case, you are now "that guy"
Hungover college student: OMG OMG OMG, I totally shouldn't have slept with "that guy" last night! What if my boyfriend finds out? He'll probably beat me and none of it was even my fault!

Friend: About that... he was also at the party.

Hungover college student: O_O
by A rabid chicken November 19, 2010