When I was a grad student, my roommate had a name which didn't sound super common, but there were actually at least three grad students with the same first and last name at the same time; and two in the same department (let's call it Underwater Basket Weaving). My roommate (let's call him John A. Smith) kept getting in trouble because of this other person (let's call him John T. Smith). Once was when John T. Smith helped make an Onion-style parody paper that included sexual innuendo from a bunch of professors (including one on my roommate's thesis panel). Another was when John T. Smith ran up some sort of debt and didn't pay it, and the collections agency managed to find my roommate's information. He had a hard time convincing them that yes, there were indeed two John Smiths getting their PhD in Underwater Basket Weaving at the same time, and he was the wrong John Smith.