Frank opening his pants each time he sits down?

People sometimes undo their pants when the are bloated after a meal. The ever-uncouth Frank does this routinely, in front of others, reminding us that he really doesn't care what anyone thinks about him. This was a running gag that appears to have been originated by the creators of the show.

In a book about the creation of the series, You're Lucky You're Funny: How Life Becomes a Sitcom, Phil Rosenthal writes about the casting of Frank Barone. They were looking for a "nonethnic ethnic" to contrast with the more ethnic Italian/Jewish Ray Romano and Brad Garrett. When Peter Boyle arrived for the audition he was furious because he had had trouble finding the place.

He scared me, and I gave him the part.

He happened to be funny, too, when he calmed down. But we saw that we could use a little of that anger... Lucky for us, he was also hilarious at sitting in a chair with his pants open and rifling one-liner at his wife, his sons, and anyone else in range. We had the father.