Joan Rivers -- Anthony Weiner's a 'Piece of Garbage'

Joan Rivers tells TMZ ... she doesn't believe Anthony Weiner is fit to hold public office ... 'cause he's a total "piece of garbage."

Joan was in NY yesterday -- and wished us a happy Rosh Hashanah -- when the topic turned to the most famous Jew vs. Jew battle since Cain and Abel ... Anthony Weiner vs. The Jewish guy in the deli.

"[Weiner] was like, 'Don't judge me!'" Joan said ... adding, "No, we don't, we just judge your penis."

There's a pretty good "pulling out" joke in the clip too. Check it out.