A man walks into a pharmacy and asks for a pack of condoms. As soon as
he has paid for them, the man starts laughing and walks out. The next
day, the same performance, with the man walking out laughing. The
pharmacist thinks this odd and asks his assistant, if the man returns,
to follow him.
Sure enough, he comes into the store the next day, repeating his
actions once more. The assistant duly follows. Half an hour later, he
"So did you follow him?"
"And...where did he go?"
"Over to your house..."