I doubt the MixedMetaphor needs any introduction, but examples can be fun.
Someone I work with, in a meeting the other day talked about being "down to the last wire". A German fellow in the meeting asked what she had said, so she repeated it in all earnestness "down to the last wire" (not putting her down, you understand - I've been guilty of worse).
My wife is famous for mixed metaphors which she never knows she's saying and only recognizes later. We've laughed about some of them for years - especially "That was the last needle on the haystack." If you think about it, that's actually mixing 3 metaphors. Also - "It was the worst craw in my side."
I HaveThisPattern too. --GunnarZarncke
I smell a rat. I see it hanging in the air and I will nip it in the bud. -- traditional
See also PrivateEye's legendary "Colemanballs" column: http://www.compsoc.man.ac.uk/~heth/funnies/coleman.html