Montezuma's revenge, Aztec two step, mummy's tummy, or Cairo two-step in Egypt, Kurtz Hurtz in Uzbekistan, Bombay belly or Delhi belly in India.
A case of the sh-- or Hershey Squirts or The McSh-- in North America, Down Under Butt Chunder in Australia, Karachi crouch in Pakistan, Suryavarman's Revenge in Cambodia.
Kabulitis in Afghanistan, holiday tummy in United Kingdom, Bali belly in Bali, or Taghazout Tummy in Taghazout or Kathmandu quickstep in Nepal.
Beaver fever in Canada, Thailand it's Thai-dal wave. Peacekeepers to Arabic-speaking countries have called it yalla yalla (Arabic for "fast, fast").
In Central Asia, it was ridiculous, with every second backpacker walking around with toilet paper on them, regularly having to make a 'run' for it. In Egypt, half my tour group got sick, by the time we'd converted into a mobile pharmacy!
Regardless of what it's called, what's the best way to try and prevent it?