Oz was a real jerk in this
I get that both his girlfriend and Heather's boyfriend were dodgy people but that doesn't make it alright for Oz to completely screw them both over the way that he did. They are both supposedly in long term relationships but Oz thinks he can just waltz up and take Heather straight back because they dated for a long time during and after high school? He took it upon himself to go and kiss her before he had even mentioned his problems to Mia and then he just starts kissing Heather again at the reunion with her boyfriend a few metres away??? What the hell! Ok so the Dron guy was a bit of a tool but he hadn't actually done anything that wrong, but we're supposed to cheerlead Oz screwing him over and Stiffler knocking him out?
Also Oz was all a bit up himself over his job and his dance off show, supposedly over that weekend he's suddenly become really ashamed of his whole career and everything he's done? Was there supposed to be some sort of implication that he'd been on drugs before with Mia taking E's and him being off his face on the dance off show?
I dunno, overall I love this film and think they handled it all really well, but you can see why Oz's character was deemed surplus to requirements for the Wedding