I know some of us put down phrases that really DO make sense even though the original question was about what are some that DON'T. I have never understood why "pulling my leg" means "you're kidding me.
jcraine-- I think the phrase you mention has the word "daubed" (not dobbed). To daub means to paint. Mud daubers have mud nests. A mud fence daubed with lizards is quite the word picture to describe ugly!