Not the op, but I used to be friends with someone who despised Cordelia. When she'd find pictures of her, she'd write "boo hiss." It all stemmed from her dislike of Xander/Cordy because it interfered with Xander/Buffy.

Frankly, even though I'm not a huge fan, I don't dislike her either. I found her story arc to be interesting and, for the most part, well developed. And I've yet to hear an actual reason for hating her that isn't as shallow as "But she ruined my shipppp"