Usually the life of the party. When "This Guy" (or occasionally "That Guy") walks in, you know shit's about to get good. He's liked by everyone, has killer dance moves, and just all around fucking rocks out with his cock out. He has the funniest stories, the dirtiest jokes and can swoon any lady he wants.
Usually is wearing something suave.
Occasionally could be a Garden Gnome.
This Guy: *walks into party* HEEEEEY guys!
Everyone: AW YEAH THIS GUY JUST WALKED IN!
What you say when someone does something stupid or something to draw attention to themselves in a less than desirable manner. Usually accompanied by a single or double underhand point and no other verbal context.
A way someone refers to another person (the subject) in third person, implying their opinion of they are simply amazing or a downright retard. It is usually in a conversation after the incident had occurred.
Person 1: Did you understand the movie??
Person 2: Nah, this guy *points to guy 3* interrupted me
¯\_(ツ)_/¯ ← is this guy. His name is this guy because no one knows his name. He is the whatever face you see on the website The Urban Dictionary when there is no definitifor a word.