Let me make sure I understand this. So when I get in the 2 hour standby line for FoP, I don't have to use the bathroom. But after waiting for any hour, I really need to. And if I leave, I'm considered cutting in line when I return and am subject to removal from the park if a CM spots me? I usually tell the people standing behind us that I'm leaving to use the bathroom. I try to remember to tell the CM at the entrance. But Disney would rather I remain in line and pee in my pants? That explains why parents let their kids pee in line....
Or maybe when you leave to use the restroom, the CM at the entrance can hand you the Disney version of the bathroom hall pass.