I used to have a friend who seemed to think that since her grandparents were German, she automatically knew the language. Also, since she knew a lot of Spanish speaking people while growing up, she thought that meant she automatically knew that language as well. Granted, she knew a few words of both languages, but that's all-a few words. (Think Peggy Hill on King of the Hill, except friend wasn't nearly as fluent as Peggy).
This led to much hilarity, especially when dining at a Mexican restaurant. She would sometimes insist on ordering in Spanish. That would have been fine, except the servers usually didn't know what she was talking about. They would keep asking her to repeat her order until she finally gave up and told them in English.
She wouldn't let that deter her, though. When things like that happened, she would explain to poor, stupid me that the server must speak a particularly odd dialect and not "traditional" Spanish.
She also had the annoying habit of adopting a fake accent whenever she was around anyone with a genuine foereign accent. She and I had been planning a trip to England at one point but I backed out when I realized she would have spent the entire trip trying to talk like the Queen.