Imodium D. It's an over-the-counter remedy and your chemist should have some.

Cheese is a folk remedy.

Paragoric and other opiates will also work, but they are probably only available by prescription.

If it goes on too long, call the doctor. It's funny, but it can weaken and even kill you. I'd also suggest a sports drink for electrolyte replacement (or just mix up sodium bicarbonate and salt in water).

As for euphemisms: the trots, the runs, the two-holer two step, green apple trot, Montezuma's Revenge....