I didn't hate Parker. I mean, yes, he was a real jerk, but, in spite of what Buffy fans tend to think, he wasn't evil or anything like that. He was the typical douchey college guy. What I hated was Buffy's reaction after he used her. I mean, sure, you could argue that all of the men she had become accustomed to were fairly romantic and cared deeply about her (Angel was the ultimate melodramatic boyfriend, and Xander, though preoccupied with sex, did respect her), but she should have known that a good percentage of college guys just wanted to hit it and quit it.
So overall, I'd give myself a 3 on the hatred scale.