I'm sure most of my readers already had to cut onions at least once in their life and had to cry because of that. Well, my ingenious brother found a way to reliably avoid that (and it indeed works, I tried it out today):
Get a big piece of cling film, and wrap it around your head so that it covers your eyes. Be sure that you're still able to breath through the nose! Then start cutting your onion(s), and you won't experience any more crying. The only disadvantage is that your look through the cling film is not as clear as without, but to be honest, who cares as long as there is no more crying involved?