|1.||Who's this guy?|
1. A phrase which can be used to humiliate a person who you know well, who has just said something that has either failed at telling a joke, or has just said something stupid or embarrassing.
2. Said when there is a stranger nearby acting in a funny or weird way, or who complies with the above.
Both are generally said with a thumb in the direction of the offender, and a generic "pfft" noise.
Charlie: I've got one of those!
Ollie: Pfft... Who's this guy? *points thumb towards Charlie*