Whenever something really turn you on, hooks you, intrigues or interests you, that thing "fucks your shit up." Only use for major things, not minor things; i.e., you wouldn't say "Cheetos fuck my shit up" unless they literally feel orgasmic in your mouth. And, yes, this idiom allows sarcasm. *Can be referred to as an acronym, FMSU.

A casual invitation / threat used by an individual that is not afraid of fucking someone up.