You're allowed to give yourself a nickname, of course.
But not for others, unless you want to piss them off. And definitely nothing cutesy.
*pats self on back, for not calling Michael "Mikey"*
*admires own self-restraint*
Discussion
Gosh, I love this team. 💚🤣
Proper nicknames are not a common variant of your given name. I knew a guy named Steven, he told everyone to call him Steve (not a nickname just a chosen variant of his name, this is acceptable for you to choose) we all called him Skeeter (a nickname)
Had he had a choice for his nickname I'm sure he would have chosen something superficially manly like bear. He doesn't get a say in his nickname for exactly that reason. His nickname came from a collective judgment and agreement of those who knew him. This kind of nickname you are not allowed to self appoint for any reason. Attempts to do so will be seen as extremely cringe.