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: It's fatness, plain and simple. It's a person becoming fat before your very eyes.
Charlie: And I don't even know how to make the bird jokes anymore. They no longer apply.
Dee: I'm not fat, I'm pregnant!
Mac: I feel like you say that all the time now.
Frank: You better do yourself a favor and flush it out.
Charlie: Wait a second, you definitely said that before.
Mac: Since we're all saying things we say all the time. I'll just reiterate. Dee, we don't care about you, or your body, or that baby bird.

Dee: Just so I'm clear, you don't actually think things are going to come alive because you're spending the night in museum, right?
Dennis: I'm sorry, we're simply opening ourselves up to the possibility of an amazing adventure this evening. Is there something wrong with that? Whether that means Charlie running into his ancient spirits or us running away from security guards all night, it's gonna be a really great time.