When they decide they have to ship the main characters. It always destroys shows. X-files went off the deep end when they decided to put Mulder and Scully together. Same thing happened with Bones. It destroys shows. Men and women work together IRL for years without ever ending up in bed but no one on TV can do it apparently.
When they save the world for the 3rd time. SUPERNATURAL
When the funny stupid character becomes a total asshole, examples being Patrick star and Peter Griffin.
When they decide they have to ship the main characters. It always destroys shows. X-files went off the deep end when they decided to put Mulder and Scully together. Same thing happened with Bones. It destroys shows. Men and women work together IRL for years without ever ending up in bed but no one on TV can do it apparently.