At the end of your trope

So, all you writers out there: have you ever been tempted to hang a lampshade on  a weak point in your plot?  Have you ever been reduced to the use of oven logic?  Or do you have no idea what the hell I'm talking about?
If the latter than you might want to discover a cool webpage called TV Tropes.  It is a wiki and, as the home page explains, it is "a catalog of the tricks of the trade for writing fiction."  Don't think it is limited to TV, by the way.  There are plenty of examples from literature, movies, comic books, and even video games.

If I have a problem with the execution it is that they love clever names for the tropes, which can make it hard to find the one you are looking for.  (If you find one that is almost what you are looking for, check the related tropes at the bottom.

Here are a few of my favorites.

Absence of Evidence  In mystery fiction this is known as the dog in the night-time. 
Black Best Friend  Doesn't need much explanation, I guess.
Bolivian Army Ending  As in Butch Cassidy.  Nobody here gets out alive.
Bond Villain Stupidity.  I found this one in the index by typing in "Goodbye, Mr. Bond."  The villain (not necessarily in a Bond movie) at long last captures the good guy, sets up an elaborate death trap, and then doesn't stay to see if it works.  The movie Austin Powers mocked this perfectly.
Bus Crash  A character is killed  retroactively, that is, after the actor has left the show (and therefore doesn't get a dramatic death scene).  Most famously, I think, Henry Blake on MASH.
Crazy enough to work  As the wiki noted, this is practically Captain Kirk's middle name.  I hate when it shows up in a story, but what about when it happens in real life?  Apollo 13, anybody?
Lampshade Hanging You have a plot point so weak or unlikely the audience may refuse to bite.  So, illogically, you call their attention to it.  As the page points out, even Shakespeare hung a lampshade or two.
Mr. Exposition  Hello, hero.  Let me tell you everything that has been going on, which you probably know, but the autdience doesn't.
Oven Logic  Old comedy  premise.  We need to cook it faster so double the temperature and half the time!

Red Shirt Army  If you ever watched Star Trek you understand this one.  Why can't the storm troopers ever shoot straight?

Tomato Surprise  A specific kind of twist ending, one that depends on the audience suddenly learning something that some of the characters have known all along.

And finally....
Not worth killing   The bad guy lets the puny mortal go, as not worth his attention.   But what I was looking for and couldn't find was the situation where the hero is about to destroy his career/violate his code by killing the bad guy in cold blood and the side kick says "Don't do it!  He's not worth it!"

I hope you find TV tropes to be worth your time.