IIRC he flat out admitted he ripped off Eltingville.
Bill is really a classic case of a mediocre person longing for power and respect. Josh is set up as the real asshole of the series early on, because he's quick to anger and portrayed as selfish, but it's of course Bill who is revealed as the big bad, starting when he uses his trick die on the others, down to when he dissolves the club because he got a job at the comic shop. Pete acts like a dick, but isn't really much of one outside his opinions. Jerry is just along for the ride mostly. Josh is mostly just dimwitted.
You have to remember that Bill is the only member of the group who didn't make anything out of himself. Jerry's a rising MtG player, Pete got to join one of his horror porn producers, and Josh actually managed to get a press pass the hard way. Bill started a business that was just an excuse to read other people's stuff.
Also remember that his rant against Jerry's girlfriend came after he got mad that the others might make him look stupid in front of her, which was after he was flustered that she was there, which was after he made a bunch of lewd comments about her as she walked up. If she had walked up to him and said he was cute, he'd be sucking her toes if she asked. His anger and his supposed truth, accurate as it may or may not be, is not a steadfast belief, but the lashing out of a guy who has mixed his unluckiness in life with a disproportionate amount of selfish, antagonistic, flat out assholian behavior.
And therein lies the warning not to be like Bill, a nerd and a virgin and unable to succeed past controlling three other losers, but also a thief and a misogynist and an asshole who dropped those three losers first chance he got.