I Forget ... Was It All a Dream?

In the course of dinner tonight, I mentioned the plot for tonight's Mentalist, which involves ... amnesia.  This led to a family discussion of which plot devices are most annoying.  Yes, this is the Spew Family at play, discussing such things as poor writing devices.  Nerds are us.

Anyhow, we came up with three truly annoying devices and disagreed over the ranking:

• Amnesia.  So incredibly annoying.  It allows writers to allow their characters to, well, lose their character as they then can act in ways that forget the lessons they have learned.  Only Memento did this well precisely because it was entirely about amnesia and learning who this person really was, rather than conveniently forgetting what made this person be the person that they were.
• Clones.  This is such a lazy recourse for science fiction--a character gets killed, but once the writers regret doing that, hey, we have a bundle of clones.  No, this is not what doomed the Star Wars prequels since clones as cannon fodder is fine.  No, it is the "hey, everything you thought for the past x years is invalid since it was just a clone" device.  I stopped collecting Spiderman in the mid 90's when it appeared to be the case that there were multiple Spideys and the Peter Parker we knew was not really the original Peter Parker.  And Gwen Stacy was alive and Jean Grey was alive and all the rest of that. 
• Dream.  It was all a dream.  Another cheap way out for a writer that sets on a path and then regrets making tough decisions.  The exemplar is, of course, Dallas.  But this happens elsewhere.  The only case it really worked great was the last episode of the Newhart show. 

I guess I mind Amnesia the most since it is probably the most abused--that it applies well beyond science fiction and fantasy whereas clones tend to be restricted the most nerdy literatures/movies.  Of course, if Community uses any of these to make fun of these devices, then it is ok.  Otherwise, it usually is a sign that a writer wrote him or herself into a box or otherwise is bereft of ideas.

What is your least favorite plot device?