Is it normal for a girlfriend to change a guy?

A good friend of mine, lets call him jerry, got a girlfriend. Its his first real gielfriend, and ever since theyvw been dating he'a been different. He used to be so humble, good at everything, yet kept quiet. Never a dick. Now everytime we hangout he's kindof an asshole. Ill say something about my stick shift car and he immediately just attacks my words and tries to dissprove everything i say, and im not wrong so it makes him look like a total douche. I feel like ever since this giel has been here he'a gotten this extreme self confidence boost and its really turning him into a dick. Idk what to do, i wanna tell him but he's really happy with this girl. Honestly he's a homie but if he's happy being an asshole to his friends than so be it but its not even hurtful its just embarrasing how ignorant he makea himself seem. Any tips or suggestions? I want my homie back