For the two aspects I mentioned, for pissing, there's no need to
accidently zip the bird, as there's no zipper, just gently lift up
the skirt and push either down or to the side the undies and out
comes the bird pissing... As for passing motion, no need to push
the skirt down, just take off the boxers or undies will do...
One more thing, doing it with clothes on, a skirt can be useful
too... helps for easy access as well as cover... 
