Here is my idea, get an icy hot patch and take the gel inside and put it on the toilet seats. some dialouge of how it might happen:
person 1 (washing hands)
person 2 AHHHHHH MY ASS AHHHHH!! (hits stall door)
person 1 What the!.................. Its ok man just let it out.
person 2 (continues to scream and hit the door)
person 3 What the heck is going on here?!
person 1 he's just having a little bit of trouble.
(bell rings) person 1, 3 leave and person 2 is still in the stall