Selene, the main character in Underworld. Haldir as well. Both of them because of things that happened in RP. Even though I have a reason, I still think it's a bit irrational to dislike the original characters.

Tauriel is not irrational, but I dislike her for very shippy reasons.

Solas however is irrational, because I haven't played the damn game and I merely hate his face.