It's not quite a nickname, but before Sheriff Stilinski got a canon first name (he is literally called Sheriff, Sir, or some form of Dad for 6 seasons), a lot of people in fandom gave him the fanon name of John. His name turned out to be Noah, but there's a lot of fic writers that insist on still calling him John (there's a tag), and I just roll my eyes at them. I do acknowledge that TPTB share a part of the blame for waiting so long to give the character a first name, but damn, I'm pretty sure they're not really sticking it to the man by keeping one of the most common English male given names.