Now my own grandparents spoke Yiddish. Sure, they also spoke Hebrew (at least the three I got to know, but I assume the fourth, who died in Jerusalem in 1941 also at least dabbled in it). They were also fluent in Russian on one side and Polish on the other. And there is some evidence that German, Romanian and English were also within their collective repertoire.
I never really cared for the Slavic languages they spoke. Of course, this was before I became a professional linguist. But with Yiddish I had sort of a love-hate relationship. I was never taught the language. Moreover, I was socialized to believe that I shouldn't know it. It may have been my paranoia, but apart from terms of endearment, such as ingale 'boy', ziser bukher 'sweet guy' and royte bekalakh 'red cheeks' (of course they're red, grandma; you just pinched them with all your might!), I felt that Yiddish was only spoken around me as a secret language. Only grownups (and not even all grownups) could speak and understand it. Being the smartass – or uberxuxem - that I was, in hindsight I would have expected myself to force myself to learn it and be my own little intelligence agency. But I guess I was too lazy. And too pissed. You don't want me to understand? Well I don't wanna understand you anyway!
Years later, when I only had one living grandparent left, I decided to take interest in Yiddish. I audited a Yiddish class at Penn, and in a dialectology class with Bill Labov, Hannah and I did a little research project based on Weinreich et al.'s