I absolutely have to pass on this AskMetaFilter comment by the learned and much-traveled polyglot zaelic; one begins to get a feel for how he came by his polyglottery:
In my family, when we spoke English we were generally being nice. For the nasty backbiting stuff we had a pool of languages that would always leave somebody out of the loop – Hungarian, Yiddish, Romanian, Russian, and Spanish. I learned Romanian completely through the bitter invective of my Grandmother, who hadn’t taught it to her own kids, who in turn, used Russian as a secret language of hate. As adults it came as a surprise to find everybody in the family was fully conversant in Spanish — no one ever told anybody else, because it was only used to whisper nasty comments about people in private. And my Mom has just started to teach me abusive language in Turkish that she learned in the 1940s working at her family’s Sephardic Turkish restaurant in Budapest.
Wow. And I thought it was impressive that my mother’s parents could lapse into Norwegian when they didn’t want the kids to understand.
If any of you have similar anecdotes, the microphone is, as always, open.