I feel bad that this is funny to me! No offense, ok? It's just you described exactly our superstition! Sometimes you'll see a group of kids who encounter that situation will argue with each other over who has a birthmark on his bottom and it's funny because it turns into a real argument. The term is "May balat sa pwet"(With birthmark on bottom). If it's a nice day and a group decides to spend it outdoors and it suddenly rains, someone will ask who has "balat sa pwet" or on a trip and something gets lost usually at the very start or at the very end, same thing! It's actually happened to me on a trip and someone in our group had one and poor guy felt so guilty because our trip was ruined by a freak storm! I will look around to see if there is an "antidote" for your situation. it won't hurt, right?