Mad Piss
When you're so full of pee you feel like you're about to burst, and you're ready to do anything to get to the bathroom.
I had to pee so bad I walked out of my house in my pajamas like a crazy person.
During the school play, I had to pee so bad I almost forgot my lines.
I had to pee so bad I told my teacher I had a stomachache and I really just wanted to go pee.