It's a skill to be able to hold one's shit in until he/she makes it to the toilet cubicle, closes the door, pulls down his/her underwear, takes aim and Hiroshima time! If really cannot than, find a place to sit down or press your butt against a wall and stand very still. Breath slowly and think of nothing. When the shit subsides a bit, continue making your way to the toilet, and don't think of anything that'll excite you.