Oh hell no! You are not changing her massive butt! You eat your burger before you are left with that responsibility! You much down as fast as you can as you sister giggles at you, you can feel it's mind numbing effects but you don't care.
You'd much rather be an idoit that deal with her diaper even as you feel your control leave you and you start pushing a load into your pants. You can't help but giggles as what little remains of your burger gets all over your face and your diaper warms again.
Then someone comes in, who is it?