Kyle receives an obscene and vulgar prank call from an anonymous caller (Cartman) but instead of hanging up like a normal person he just keeps yelling at him back, and then even ends up descrbing in detail what he's going to do to him. Cartman is into it and they end up jerking off

Bonus if later Kyle's roommate (Stan? Tweek?) emerges to ask about just who the fuck he's been talking to for the last hour and a half and why he didn't just hang up