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When you tune in to the seventh-season premiere of "It's Always Sunny in Philadelphia" (Thursday, 11 p.m., FX), do no adjust your set. Hunky Mac (Rob McElhenney) really is, um, large.

He's fat. On purpose. He gained 50 pounds for the show. On purpose.

The idea to gain 50 pounds came to McElhenney "when I was watching a very popular sitcom, and I noticed that the people were getting better-looking as the years were going on. I think mostly because they were more famous and they had a lot more money, and they got new hair and new teeth and a new trainer."

The idea behind "Sunny" has always been to be sort of the anti-sitcom.

"Instead of making the characters as likable as possible, we've always tried to make them as unlikable as possible," McElhenney said. "So I thought maybe the same could be done with the aesthetics. So I thought it would be really interesting to watch somebody purposely try to look as ..."

"Bad," said Kaitlan Olson (who stars as Dee).

"Unhealthy," added Glenn Howerton (Dennis).

"Sloppy," added Danny DeVito (Frank).

Although not necessarily unrealistically so.

"The reality of five people in a dive bar in South Philadelphia is that they won't get better abs as the years go on," said Charlie Day (Charlie).

"And, like, I'm being realistic in terms of the way that the character would look based on the way he eats and drinks and doesn't work out," McElhenney said. "This is close to what he would look like. It wasn't just about the weight gain, it's also the beard, and my hair was really greasy, and I tried to look as ugly as possible, basically."

Not that the character is aware of any of this. He thinks he's been putting on muscle.

"Mac believes that he looks fantastic," McElhenney said. "That hasn't changed."

McElhenney is losing the weigh. His only regret is that his castmates didn't join him in his devotion to his character.

"Well, what he first said was, 'We should all gain 50 pounds for this season,'" said Olson. "And we said, 'No.'"