You suck big donkay balls! How do I know this? Well, it's several things. One, you never clean up the donkey when you are done, and the dried saliva makes him itch. When the donkey then tries to scratch, making it look like he is humbing the fence, it leaves him very chafed and irritable. That, and it leaves ass hairs on your face.
Perhaps you should suck your own balls instead. This would greatly improve your flexibity, and would be a great party trick. While I'm sure your balls are not as "fullfilling", it would be the kindest thing to do.