He looks so pale and sweaty in that picture, his anxiety definitely seems to be getting worse. I wonder if his lack of a suit is making him more anxious than usual. Like it's a security blanket for him.
Like with the car thing, he's stuck operating under a rigid set of rules that he learned in high school and can't let go of, due to a combination of crippling mental rigidity and inability to admit error. "Guys without cars are dateless losers." "Virgins are losers." "Fat guys are losers." He's clearly absolutely terrified of people thinking that he's a loser, so he has to let people know that he's obeyed all the not-a-loser rules. But because he is utterly socially inept, and has absolutely no theory of mind, we get this series of weird flexes.
I can't help but think that he was bullied a few times, maybe even just once, and was taunted as a loser at the time. Yes, members of his faith are generally nice people, and most people in general try to be kind to the retarded, but not everyone is like that. And knowing what kind of person Russ is, there had to have been occasions where, being himself, he just couldn't help pushing things too far. Maybe this was the occasion when he was shocked to find out that he was not in fact popular, possibly after having this fact kept from him for his whole life up to that point. And this was traumatic for him because of his anxious nature and inability to let things go. And he's been secretly terrified of looking like (his idea of) a loser ever since.