Roseanne Barr
No one will forget Roseanne Barr's fall from grace. She had an extremely popular show that was a revamp of the original show that got her popular. The public loved it, but Roseanne had to go and ruin it by tweeting out racist things about Barrack Obama's former Senior Advisor.
Racial Divide
To make it worse, she fought people on whether or not she was acting racist and then continued to say more racist things. ABC swiftly canceled her season and revamped the show without her. She's been blacklisted ever since.