>Yiddish arose as a street language compared to Hebrew, didn't it? As this was explained to me by a Jewish neighbor, it was more of an intentional bastardization than an inability to get the words right. Kinda like rap. (Lord, there's a thought, Jewish rappers).

Not exactly. Yiddish was the language of Ashkenazi (i.e. German) jews in the Diaspora in around the 13th Century or even a little earlier. Not really related to Hebrew except that for the last few centuries has been written using the Hebrew alphabet. If you want to consider it a bastardization, it would be from German not Hebrew.