Some characters aren't happy just using their superhuman powers for truth, justice and the American Way. They also apply them for... recreational purposes.
Please, examples shown in-universe only. To speculate falls under Wild Mass Guessing.
See Rule 34. Shapeshifters Do It for a Change is a related sub-trope. Fantastic Arousal is when this trope meets unusual body parts. Extreme cases of power [...] [tvtropes.org]