Historically, all that has prevented Peter from being a total dick is his willingness to admit when he's wrong. But he can get pretty fucking self-righteous and, though I'm not fond of OMD(if you're ending the relationship, dramatically end it, don't erase it, that's just lazy), I really have no idea why MJ ever stayed with him more than six months. Gwen was perfect for him: pretty, one-dimensional, and safely dead.
And when smoking comes into it, Peter can REALLY be a prick, but I think in his case, isn't it also to do with his having more sensitive senses? Or that the smoke fucks with his spidey-sense or something? (it could; smoke carries an electrostatic charge, which incidentally is why it often graviates to nonsmokers)