Okay, maybe this won't go anywhere, but this is not so much a "trope" as a concept, or a rule.
Basically, any video game that has a level editor will inevitably have a NSFW-themed level.
- Wario Ware DIY lets you make your own "microgames", and it wasn't long before people made ones themed after getting boners.
- Little Big Planet quickly got penis-themed levels shortly after launch. There was a You Tube video of a level in which you rode a giant penis with rockets attached.
Anyway, maybe this article wouldn't be filled with examples, but maybe it could work as a "rule", similar to the existence of "Start To Crate" and "Rule 34", etc.