after sexual intercourse, the semen dries on the tip of the penis and seals it. This goes unnoticed until the man decides to pee. When standing over the toilet and starting to go, this seal is partially broken and you end up peeing all over your leg and the floor.
It is the same effect as pinching the end of a garden hose to make the stream change direction.
Her: "Why is your pee all over the bathroom floor? Can't you hit the target?"
Him: "It's not my fault, I had garden hose syndrome."