Cast your vote here. It could be anyone: villain, crew, member of the admiralty, etc.
I have to say that Berlinghoff Rasmussen is possibly (IMHO) the most obnoxious character in any episode of any ST franchise series. I especially hate the way he addresses the Captain as 'Picard'. So disrespectful in a smug, smartass sort of way. Just once, JLP should have assumed his vengeful god persona and said, "It's Captain if you please."
Well, for me, the most unlikable character in all of Star Trek has got to be Neelix. For TNG, it's Okona.
Among the cast, I don't detest anyone overall. I have my particular issues with Riker and Picard for their performances as officers, especially Riker, whom I expect more out of. I think Worf is something of a hypocrite, a guy who loves the Klingon Empire and wants so much to be thought of as a Klingon warrior, but does not up and return to the Empire to prove himself as one when he had more than ample enough opportunity to do so. And, of course, Troi is written terribly. That's the main issue with my faults with these characters, that they are written so terribly because they were ill-conceived from the start.
I never liked Chakotay from star trek voyager or B'Elanna Torres. Chakotay in particular always had so many plots revolve around him. What was that about.
Troi. Who the hell does she think she is, always prying into people's business (I realize it's her job, but it's intrusive and annoying), and why does she get to wear that stupid leotard instead of a regular uniform like everybody else? Picard should have dropped her wide ass off at the first starbase they passed.