Lampshaded: "There goes Bob's pants again. We should have known that he'd keep them somehow."
Invoked: "Once I gained my powers I knew I couldn't just run around naked, so I made myself a custom pair of baggy pants to stay intact when I grow. Just like in the comic books."
Defied: The villain disables the magic pants first so that Bob, out of modesty, will not grow.
Discussed: "I have no idea. I'm just glad they don't rip."
Conversed: "Why do characters in these movies always keep their pants intact? They must have Magic Pants!"
Deconstructed: Bob's Magic Pants are made out of incredibly stretchy material. Once a rogue scientist manages to get a sample and analyze it chemically, he starts a company selling the stuff and drives the entire clothing industry out of business, making millions of people jobless.
Reconstructed: However, a new industry arises out of the chaos, hiring those people back and selling very nice magic pants.
Played For Drama: The pants are cursed and will eventually kill Bob. His attempts to destroy it are failing and if he fails his daughter will be left orphaned. Thus their staying intact when growing is a crushing failure.