Two blondes fishing

Two blondes rented a boat and went fishing. After finding a good location, the first blond told the second one to mark the spot so when they came back they will be able to find it again. On the way home, the first one asked, "How did you mark that spot?" The reply was, "I put an X on the bottom of the boat." To that, the first blond said, "You idiot! How do you know we'll get the same boat next time?"