Postal 2

Moms love animals. Most of them do, anyway. It's probably not a good idea then to show off a game that lets you shove a cat's ass on the end of a shotgun and use it as a silencer.

Maybe your mom's the type that absolutely loathes animals and she'd find it funny, but even in that unlikely event there's still all the pissing and dismembering in Postal 2 she'd have a hard time swallowing.