TNG: Pulaski, for being such a needless bitch to Data. Tasha Yar was pretty bad, but at least the sludge monster got rid of her. Any early ferengi.
DS9: Keiko - as if Miles doesn’t have enough problems being tortured every few episodes without this harpy waiting to nag his ear off every five minutes. Kai Winn for being so smug it hurt and conjuring up hideous images concerning her and Dukat. So glad she got roasted in the season finale.
Voyager: Chakotay, for being utterly pointless and phoned-in performances. That dumbass kazon who hung out with Seska. Neelix for obvious reasons.
Enterprise: Didn’t watch much of this one, but Archer and Tucker seemed like colossal prats in the bits I have seen.