When on vacation in a foreign country: If someone tries to talk to you, look confused. Wait for the person to repeat themselves in different languages, and continue to look confused even when they say it in English. When they finish, start asking questions in a made-up language. (Stranger: "Hello, do you speak English?" Respond: "Dbada doola pandooo dada-achka lmkta?")

Actually, this someone at my school did this when they were on vacation.