I am generally very forgiving. There isn't much a game can do to annoy me.
But, what I really don't like is - wait for it -
I hate that. It's okay when there is one ending for playing a good character and one for playing an evil one (as I NEVER play evil) but I hate it when a game has multiple ending based on some hidden things you do or whatnot.
Also, in the same vein:
I hate it when a game requires you to play it multiple times to experience the whole story.