I marked the spot

Two friends rented a boat and fished in a lake every day. One day they caught 30 fish. One guy said to his friend,

"Mark this spot so that we can come back here again tomorrow."

The next day, when they were driving to rent the boat, the same guy asked his friend, "Did you mark that spot?"

His friend replied, "Yeah, I put a big 'X' on the bottom of the boat."

The first one said, "You stupid fool! What if we don't get that same boat today!?!?"