Those are good ones try this one

Once there was a sperm named Bob. When all the other sperm were just swimming around, Bob was doing sprints and lifting weights all the other sperms asked him one day, "Why don't you just swim around like us?"
Bob replied, with a smirk, "well, when the time comes, I'm gonna be the first one there".
The others told him it was just destiny, but he said it wasn't. So, the day finally came when they were called upon. They were swimming along when Bob pulled ahead of the rest. Suddenly he stopped and turned around and headed back.
The others asked him why he turned around and he said, "back up boys it's a BLOW JOB!"