Yellow Teeth?

Well here you are your stuck in a bathroom with nasty build up on your teeth because you forgot to brush, and lets face it you don't have a tooth brush just lying around so this may seem a bit unorthodox but it at least degunks your teeth
1. Wash your hands and fingernails thoroughly
2. (The nasty part) with a paper towel scrape off as much gunk as you can with your fingernail covered by the towel
3. Thoroughly rinse with water
4. (Optional) Take a piece of minty sugar free gum and rub on smooth surfaces of teeth (discard) rinse and you are ready to go!
HAPPY HACKING!