A new genetic mutation.

[Grek]

You know how geckos detach their tail when they're afraid and regenerate it over time? There should be a mutation that does that with spaceman butts. Any time the character does the *scream emote, they have a 50% chance of their butt plopping off and (if possible) wriggling away in a random direction for a while. Any time the character lacks a butt, they have a 0.01% chance each life cycle to grow a new one.