Call it a jinx, call it tempting fate, call it whatever gets you cooking but it doesn't make a cunt of a difference mate, there is no such thing. I guess if you believe that there is some sort of almighty force working the pieces in this giant elaborate game of chess we call life then you should refrain from booking holidays. However, I suggest you look at the facts, way up the probabilities and book your time off. If it doesn't work out then it will be nothing to do with your work rota, I can assure you.