9. Leonard Cheats On Penny - Big Bang Theory
What made Leonard from The Big Bang Theory such a likeable character to audiences was how relatable he was: chasing after the gorgeous person across the hall from him and never knowing if she felt anything at all for him was something everyone has experienced after all. So when he does finally manage to bag the girl of his dreams, fans were probably all happy to see this sweet and dorky guy do all he could to keep a hold of her.
As it turns out Penny should have dumped Leonard so many times over the course of the series. However, there was one moment in particular that undoubtedly caused every fan of the show to jump off the 'Team Leonard' ship.
Literally on the way to their wedding, Leonard decided that it was the opportune time to tell his would-be wife that he had in fact cheated on her with a girl called Mandy Chow on a voyage. The double whammy of the obvious betrayal and impeccably awful timing is one thing, however what really drove fans away was the fact it rounded off this character's transformation from underdog hero to nasty slimeball.