"Whitest Kids U Know" explained on Fuse that there's one sentence - and any variation of that sentence - that you really can't say in America.
In fact, depending on how you say it, it's "insanely illegal. Ridiculously, horribly felonoius! They will come to your house in the middle of the night and they will lock you up."
Please be aware that the contents of this video are intended as satire, and it is not presented in a way that should be taken seriously.