I know, that's what annoyed me about school. One time a teacher said this to me at 2:45pm "Why didn't you go at lunch?" I said "Well, I didn't need it 2h 15 mins ago!" and then said, "Well, you can wait for 45 mins until the end of school". I got up and said, "I'm sure if you were pissing yourself you wouldn't hold it in, **** this!" and walked out.
I got a bloody detention.... however the head of my year sort of reasoned with me after I said, "If I have bladder problems later in life, I am going to refer back to this situation"