Maybe this shouldn’t count, because I can’t really call it a great show, but the guy that stars in First Wave is pathetic.
I can’t believe noone has mentioned Michelle Rodriguez from “LOST” yet. Great show with a lot of great actors, but she just blows ass.
According to jumptheshark.com, he’s in a league of his own.
You insult Diane Neal?
Pistols at dawn, you blackguard!
I think most Lost fans would vote Michelle Rodriguez’s Ana Lucia as the winner in that show. She is wooden; at least some part of her backstory makes up for this, but it is still painful to watch her spit out lines in the same tone every time. Picking up a doctor in an airport bar, engaged in a death match with an Other, atoning for just having shot another Lostie – all given in the same tone.
She neatly replaced the other candidate for the title, Maggie Grace’s Shannon. I still think Ana Lucia’s one emotion beats out Shannon’s one and a half emotion (bitchiness and emotive bitchiness), though.
Star Trek Voyager: Captain Janeway
I only ever say five episodes or so, but both her lines and her presentation of them just had her coming off as a total bitch.
“Everyone I want to hear what ideas you have and I want them now.”
“Well captain we think that if we do x, y, and z it will solve the dimensional wedgie and bring the ship back on course.”
“Alright, well I’ll give that a thought or two but for the moment we’re going to do this my way. And I’m about to tell you what that is.”
Gah.
Is it because she’s a lesbian? 
I don’t know if Callie Thorne (Det. Ballard), Jon Seda (Det.Falsone) and Michael Michele (Det. Sheppard) murdered Homicide: Life on the Street all by themselves, or if they were just contract killers for the writers.
That’s what I meant to say when I said earlier “she just blows ass.” 
Boreanaz may not be an incredible actor, but I can’t seem to keep my eyes off of him. In his commentary, Whedon kinda echoed what everyone has said, but then said he was vetoed by the women who had turned to “puddles” when they saw him act.
I know how they feel.
I agree about Michelle Rodriguez. Yikes, what a crappy, angry actress. Where’s the TMM when you need him?
I couldn’t agree more. I’m no sap, but his role drove me to tears.
To answer the OP… the actress who played Troi on ST:NG really sucked.
Elizabeth Rohm, sucky as she is, is no match for another L &O lass, the skanky Katherine Erby of whatever the one with Vincent Donofrio is(crime investigation unit?).She just seems incompetent and dare I say, she looks like she probably don’t smell too good.
I can’t tell good acting from bad acting, and usually just saying the lines is fine with me. And even I couldn’t deal with her.
Correction: it’s not David Boreanaz, it’s David Boreanaz and his giant forehead. I don’t mind watching him attempt to crease his massive brow (er, I mean, “act”) but I never understood how any female could consider him attractive.
Sweetie, if you were capable of appreciating the postmodern greatness of NCIs, we’d still be together. It’s not a near-parody, it has transcended parody. 
I came in here to mention them. And to foam at the mouth a bit, which tends to happen when I think about the god-awfulness that show plunged into when those folks showed up.
I also nominate Patricia Tallman as Lyta Alexander on Babylon 5. Or as I call her, Squinty McSucky. There were many marvelous actors on that show, and she wasn’t one of them.
Now see, I could picture Brooks being great in this situation. I think his problem in DS9 wasn’t so much that he was trying to out-emote Shatner as he was trying to out-Shakespeare Patrick Stewart.
I saw the series in pretty much reverse order so, I got the cheesy actors first and then progressed back through enlarging greatness. As such I would say that they weren’t all that bad–still better than anything on TV–just their characters were rather cheese for the type of show it was.
(Daniel Baldwin (Beau) had probably the greatest character. Clark Johnson (Meldrick) was just never able to step up and be the adorable dumb scmuck quite the same.)
If you deny the greatness of Sports Night then, sir, I challenge you to a duel! (Though I would say that McGinley’s weak, smarmy, hammy acting was actually well-cast for his small role on Sports Night as the everything-that-is-wrong-for-Dana foil to Casey)