A long one, but I've had a 100% reply rate from around 50 uses
Feel free to copy and paste:
Imagine you and I are in a grocery store. We're in the produce section. You see me. I see you. We exchange a good-natured smile. You can't help but notice something odd about me: I'm carrying a large amount of limes. It puzzles you, but you go back to your shopping nonetheless.
After a while, you see me start to walk past you. As I do so, I spill the limes all over the floor around you. Exasperated, I bend down to pick them up. I do a poor job of it, spilling two every time I pick one up. Eventually, I stop and look up at you with a nervous grin and say "I'm so sorry, ma'am. I'm no good at pickup limes."