One that used to go around was "Slicker than snot on a glass doorknob."
I had a friend with a certain genius for turns of phrase. I've heard him singing snatches of songs like "In the morning when we writhe". He'd explain something he wanted me to do for him and often had a notion of how to do it. He'd preface his dissertation on HOW by saying, "I'm not trying to tell you how to f**k your goat, but ..." and off he'd go.
"I am often asked how radio works. Well, you see, wire telegraphy is like a very long cat. You yank his tail in New York and he meows in Los Angeles. Do you understand this? Now, radio is exactly the same, except that there is no cat." : Albert Einstein