Oh, if we're going to talk about classmates...
Guy a year ahead of me, comes into med school convinced that becoming a trauma surgeon is his one true path, and as an M2 steals a trauma pager and begins to show up to all paged out traumas at any time of day or night, including when he's in class or with his pre-clinical preceptors. When people finally realize what he's doing and how he got the pager, they assume that if they just take the trauma pager away from him, he'll stop showing up. Wrong. He buys his own pager, and convinces the Trauma administrative assistant to add it to the trauma pager list and keep showing up to get in the way. Then on his third year surgical clerkship frequently would tell attendings they were doing procedures incorrectly because he watched a bunch of surgical videos online the night before and that's not how they did them.