He is doing this, because he is insecure and because he’s trying to impress himself and likely someone else you wont be able to put your finger on yet.

Tell him to stop (maybe not even nicely or kindly shock him if he’s being an ass) and immediately drop him completely, unless of course he actually admits any of that to you. Because he’ll just keep on doing this until he reaches wherever it is socially he’s trying to climb to.

Plus odds are if you do this right as he’s acting that way in-front of people, then odds are those or that person he’s trying to impress (that you won’t be able to see or figure out yet) are likely around and it will drive him crazy when because of this you’ve magically climbed there by stepping on him, when you weren’t even trying to! Imo serves him right.