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If it's a case where the character appears to be showing off their powers just to remind the audience that they can do that, it could fall under Viewers Are Goldfish.
Yeah, I guess Viewers Are Goldfish applies. But I was thinking of it as a supertrope to which Mundane Utility is a subversion - Instead of showing off their powers for no reason, they're doing housework or whatever. Is there a trope that describes superheroes using their powers for no reason, not even as an Intimidation Demonstration?
Is there a trope for superheroes (and villains) "wasting" their powers when they don't need to, just so the reader won't forget they have it? Reed Richards stretching when he's in his lab, Wolverine popping his claws during a meeting, Spiderman clinging to walls when someone goes to see him...