Great care should be exercised by non-Yiddish speakers when using Yiddish insults correctly, so I've done my homework.
Schmuck is probably the safest to use. It just means a fool.
A schlimazel is somebody with chronic bad luck. He makes his own probably.
A schlemiel is a klutz, a bumbling fool, a banana-skin finder.
A meeting of the three would probably involve a hare-brained idea from the schmuck, enacted with all possible accidents by the schlemiel, which accidents would all befall the schlimazel.
VEXED BY VOCABULARY?
PETER THE PROOFER WILL UNVEX YOU!