Fuck you.
My Russian co-worker Vadim has decided to teach his two-year-old daughter how to say fuck you to deal with strangers who come up and want to touch her. 
Earlier, he told me the story of an old Russian man he knew who lived in New York City for 15 years, but the only things he ever learned to say were thank you, and fuck you.  The man said they were all he needed to know because they could be used in every single situation he might find himself in.