A guy walks into a sperm donor bank wearing a ski mask and holding a gun. He goes up to the nurse and demands her to open the sperm bank vault.

She says "But sir, its just a sperm bank!", "I don't care, open it now!!!" he replies.

So she opens the door to the vault and inside are all the sperm samples.

The guy says "Take one of those sperm samples and drink it!", she looks at him "BUT, they are sperm samples???"

"DO IT!".

So the nurse sucks it back. "That one there, drink that one as well.", so the nurse drinks that one as well.

Finally after 4 samples the man takes off his ski mask and says, "See honey - its not that hard."