What makes a bad actor/actress?

So when you watch a film one of the first things you'll list as the reason why you liked it will be a stand out performance by a certain someone or dynamic or chemistry between couples or groups. You notice these for the good usually how often do you really enjoy the the film and you think it was a good film, but the acting was a pile of bollocks. Its rare.
Who are the actors in this world who send us into dizzying messes when it comes to there performances, and I'm talking bad dizzying messes not good?
I will be adding actors and actresses to my list often stay tuned

Nicolas Cage
I think Nic Cage is a terrible actor, and after watching a video from youtube of him "losing his shit" he really isn't a good actor. He can't do wierd like Johnny Depp, he can't do straight down the line like Brad Pitt and his action roles are more Pink Panther than Bruce Willis. Yet his films do remarkably well... The remake of the wicker man was terrible, Season of the Witch hurt like a hang over and The Sorcerers Aprentice was also pretty awful. But Kick Ass stars Cage and I really enjoyed that. It is my belief that when he steps away from the lead role and lingers in the background he is far more watchable and enigmatic. He's like a room adouriser smells good, but too much in the air and your breathing deadly poisonous fumes.

Madonna
Not quite an actress, but she has got fairly substantial back catalogue of films to count as an actress, as well as earning herself some acolades (good and bad). The good; four films Desperatly Seeking Susan, A league of their own, Four Rooms and Evita. None of these bar Evita was Madonna the lead actress, which I believe helped her rise above the critisism she normally gets. I believe she was a great addition to A league of their own and no one else could have played Susan. Evita really is her stand out, perfectly sung, and an Oscar worthy performance. But a string of really bad film didn't help her ever morphing career and even cameos in Girl 6 and Die Another Day garnered enough critisism from joe public and press. Poor Madonna, when she gets it right, it's good, but when its wrong it is oh so wrong. Never watch Sanghai Suprise or Swept Away they are moments in your life you won't get back, however I actually enjoyed Who's that Girl which was panned by critics, so might as well give it a go.