My instructor in the States told me of a student who decided he needed the toilet 5 minutes before they were due to land. To my instructors amazement this student unlocked the window and attempted taking a leak out said window.
On landing the student was led straight to the CFI's office and his career in commercial aviation ended there and then.
Unbelievable but this story IS true and has been backed up by three other instructors at the school he was instructing at back then.
VFE.