"You'll regret this..." Hajime's pride won't let him get the hell out of there without saying something of that nature. He reassures himself that he could totally kick this guy's ass if he blew off his Cover and assumed his true form, but he's just being the bigger man here and not doing that.

Yeah. That's it.

As Hajime skedaddles, he really, really regrets that his Cover wasn't a bigger guy.