A guy goes to a travel agent and books a two-week cruise
   for himself and his girlfriend. A couple days before the cruise, the
   travel agent calls and says the cruise has been canceled, but he can
   get them on a three-day cruise instead. The guy says "OK," and goes to
   the pharmacy to buy three Dramamine and three condoms.
   Next day, the agent calls back and says he now can book a five-day
   cruise. The guy says he'll take it. Returns to the same pharmacy and
   buys two more Dramamine and two more condoms.
   The following day, the travel agent calls again and says he can now
   book an eight-day cruise. Guy says, "OK," and goes back to the drug
   store and asks for three more Dramamine and three more condoms.
   Finally, the pharmacist asks, "Look, if it makes you sick, how come
   you keep doing it?"