During Harry's fourth year, he has an epiphany watching Katie Bell play games with her boyfriend, witches were just the worst. Now, Harry wasn't running for the other team or developing a misogynist streak; he still could appreciate the female form and loved being friends with all sorts of witches.
But he had realized that dating a witch was the equivalent of dating someone who had free, instant access to a professional make over. If the witch you were dating had decided to muss with her hair, you wouldn't have any warning. No span of hours she had gone to the salon.
Nope, she could just leave the room one second and be back with a slightly different shade of hair or a different braid and expect compliments. That's not even getting into what would happen if you got it wrong. Harry shuddered thinking of the consequences.
Well thankfully, that really helped narrow down the candidate list for who he was going to ask to the Yule Ball. There were only certain witches that were not going to get upset if he misspoke or trying to "test" his interest. As he applied simple criteria, such as not believing in Voldemort and his brand of insanity, that really only left one.
After all, you could always just tell a Veela they looked stunning and not be wrong.