I typed a long reply, forgot to hit send and my reply is gone lol

But yeah, we actually do use git. I was brought into the team to be the git "expert" of the team. But while I was away, not only did he delete my work, he replaced it with something that can't work in the long term and then presented it to my boss, stake holder equivalent and the non-technical testers as the final version. His implementation was "finished", mine was not and I was too angry to look at his work. So in the end, I made it crystal clear that this can never happen again and I made it super clear to everyone involved in the project that my responsibility lies in the X part, and if someone needs something done for the Y part, they are to go to my co-worker. So like a clear division of responsibility.

I also don't have the time to un-fuck up his work. I asked him to integrate certain parts of the original implementation, but he threw a tantrum and yelled that I have no right to tell him what to do. (Ok but even if I were telling him what to do, I have 6 years of experience and a CS degree on his 1 year and no formal training, so like...)