Fat Joke or Pants Joke?

Today's strip is yet another example of the broad humor that is showcased in TBL. I don't like Glady's phrasing of the question in the first panel. It's like asking someone "I've never seen you wear a hat, don't you like wearing them?" If I didn't like wearing them then I wouldn't be wearing them now. That's at least what I would think. But the big question is what kind of joke is Chip going for? Is it a fat joke or a joke about the fabric of corduroy or a combination of the two? Either way, I love Brutus' depressed face in the last panel. And I'm ashamed that the Thornapple's marriage has come to the point where Gladys doesn't remember and/or care that her husband's pants caught on fire while he was wearing them.