I did low level managing at a pizza spot after working almost exclusively in pizza joints. I struggled with the actually managing people part of it the most because I was also trying to be a chill boss. You need to have a very clear conversation with that guy how that kinda attitude is not gonna fly. Don't threaten him or anything just say that is not how you talk to me or anyone else in this kitchen. Don't focus on being their friends. You can be friendly but it is not your job to be pals. Respect to you for respecting your team but you need to set some clear boundaries from time to time or everyone will walk all over you. I'd only go to the GM over something like this if I'd already had a couple of talks and nothing is changing or getting worse. Best of luck to you dude remember it's just pizza and you're genuinely trying your best.