Sometimes when I didn't have my contact lens solution with me, and there was some irritation in the eye I used to remove the lens, lick it, and put it back on. Cleaning the lens with my saliva was somehow always more comfortable on the eye, than cleaning the lens with whatever water was available. I did have one bad experience though - I once forgot I had spicy food and licked the lens without rinsing my mouth properly. That was a painful lesson to learn!