Yea, it happend to me,it was devistating. I was in the Bahamas doin some scuba with a full head of hair, when hunger hit me, yada yada yada cool ranch doritios and now I take propecia.
You dont have to ruin your trip though, Nacho Cheesier doritos are still safe to eat while scuba diving. Although they dont offer the refreshing burst of cool ranch doritos, they will satisfy your hunger and let you keep your hair.
Another option would be to snorkle instead of scuba, that way you can see some fish and enjoy the cool ranch flavor.