Tom Cruise - over-inflated ego, and he ruined Mission Impossible for me, the movies are nothing like the series.
David Walliams - just makes me shudder
Miriam Margoyles - random swearing doesn't make you look edgy
Sam Rockwell - genuinely no idea, I just don't like him.
Kym Marsh - can't stand the bint
Not actors, but presenters I can't stand include Claudia Winkleman, Josie Gibson and Alison Hammond. CW because she tries too hard and is a classic case of nepotism in action, and AH & JG I've hated ever since they were on Big Brother.