1. Distract them.
  2. Ask for a bite.
    Usually they are so taken aback that they'll just give it to you.
  3. Pretend it's yours and that they stole it. Takes a lot of commitment and persuasion but worth it when done well.
  4. Ask them if they want a bite of yours. Hopefully they will ask back.
  5. Wait for them to go to the bathroom and then go in for the kill.
  6. Pretend you work at the restaurant and clear the plate when they're not looking.
    I love this one.