Mysterion comes back from a mission before he and Tweek are about to fuck but he won't drop the edgy persona, voice and the mask/cape. He tries to be all dommy at first and Tweek thinks it's dorky and then fucks him into breaking character maybe.
(Tweek knows that Mysterion is Kenny but idk if Kenny is aware of that. Maybe he is and yet he's still cringe, but maybe he isn't and then finds out at the end, idk which one is funnier)