I think you should contact Mrs. Obama, Dave, and inform her of the proper protocol. You're the Brit so I think it would have more weight coming from you rather than one of us mannerless uncouth Americans. I think after you got through with her, she'd never forget.
I think the next time the Prez and Mrs. hop the pond for a visit they should tape a sign to HRM's royal behind that says, "Can't Touch This".
