Lol, got this from a friend who just read on facebook

In a biology class at university, the lecturer wass discussing sperm, and commented upon the amount of fructose contained within it, at which point a young lady put her hand up and asked
"If sperm contains so much fructose, why doesn't it taste sweet?"
As you can imagine at this point the whole lecture theatre broke into laughter, forcing the girl to go bright red, gather her things and try to run out of the theatre.As she reached the door, the lecturer asked her to stop, and said
"Before you go, if I can quickly answer your question. The reason sperm probably doesn't taste sweet is because the taste buds for sweetness are on the tip of the tongue, not the back."