I recently have been delegated the responsibility of managing a 4 people team by planning the sprints, scheduling tasks, and in general "take charge" (as said by the boss).

What bothers me is there is this "developer" with a heavily toxic attitude, who feels he is above all laws and knows everything just because he joined some months ago all of us.

He is basically a human linter. When he code reviews, you can get away with any major mistake if your linting and indentation (and all that shit) is according to "his standards".

A new guy recently joined the team and was given an overwhelming task by the boss just to test whether he belongs here. (Again, wrong, in my opinion). He didn't know any of the technologies he needs to work on to complete that task but he still learnt them and got a working product. Albeit not according to our God's "standards".

Cut to the chase, the asshole dev is now mocking him in PR comments and demeaning him in every discussion. As a "team lead", what should I do? If I let it go, it'll make the environment toxic and I don't want him to get away with it. If I do take any action, I don't want to be seen as as pussy who can't take such minor insults. Please advise.

PS. The asshole developer once wrote a "friend request accept" API endpoint in such a way that when any single person accepts a request, that'll cause all pending requests (from any person to any person) get accepted. Fucked up the DB queries basically. This is just to give a perspective on what I'm dealing with here.