A guy goes to a travel agent and books a two-week cruise for himself and his girlfriend. A couple of days before the cruise, the travel agent phones and says the cruise has been canceled, but he can get them on a three-day cruise instead. The guy agrees and goes to the chemist 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 and 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. The guy agrees and goes back to the chemist and asks for three more Dramamine and three more condoms.
Finally, the pharmacist asks, "Look, if it makes you sick, why do you keep doing it?"