Angel says, I know an oyster!

Interestingly, oytser (not oyster) is a yiddish word of fairly common use. from Hebrew o-tsar, "treasure":

1) Treasure. "My child? An angel, an oytser to us both." "Our maid is an oytser."
-- but just as often used ironically to mean the exact opposite:
2) By no stretch of the imagination a treasure. "Her son? God save you from such an oytser!" "He almost ruined me, that oytser!" "Such an oytser I wish my worst enemies."

[citation to Rosten omitted hi, Max! ]