Mac tries to look cool and dresses as Viggo Mortenstein from the Lord of the Rings movies.
Charlie attempts to dress like a vampire when he puts on a Phantom of the Opera costume on Always Sunny.
Artemis and Frank have a little lovers quarrel in costume during the Always Sunny Halloween-themed episode.
A picture from the Halloween episode of It's Always Sunny episode, "Who Got Dee Pregnant?" Dee is pregnant and the guys try to figure out who the father is.

It's Always Sunny in Philadelphia Season 6 Episode 7 Quotes

Dennis: You are dressed like the Phantom of the Opera. He's not a vampire.
Charlie: He eats theater people.
Denis: No, he doesn't.
Mac: I think he might.
Frank: He does.
Dennis: Do you even know who the phantom of the opera is?
Mac: He might not.
Frank: He doesn't.
Charlie: I don't.

Mac: I browned out that evening.
Frank: Browned out? What's browned out?
Mac: It's when you drink so much that everything goes brown. It's not as sever as a black out because I remember bits and pieces. I call it browning out.