Carly Mallenbaum

USA TODAY

How do the stars of FXX show It's Always Sunny in Philadelphia keep a straight face?

Well, they don't.

In an exclusive blooper reel, see Dennis, Dee, Charlie, Mac and Frank (Glenn Howerton, Kaitlin Olson, Charlie Day, Rob McElhenney and Danny DeVito) totally break after their costar says something ridiculous.

Always Sunny's Season 10 DVD is available Jan. 5, with an extended version of the gag reel. Season 11 of the comedy airs Jan. 6.