It depends on the show. Glee I forgive a lot more than I would on other shows. I gave up on Gilmore Girls after like 7 seasons because Lorelai cheated on Luke and refuse to even watch the episodes I love in syndication but I hate the direction Supernatural took 2 seasons ago and still watch it every week.

It's kind of a personal thing and probably depends on how invested you are in the show/character that is pissing you off.