Not to mention:
Over-act much?
“But I was going to Toshi station to pick up some power converters!”
(And yes, I’d consider Mark Hamill an “otherwise decent actor.” Only decent, but decent nonetheless.)
Thora Birch as Jane Burnham in American Beauty: “They’re trying to, you know, take an active interest in me.”
It just doesn’t ring true, maybe because the “you know” is set off too much from the other parts of the line. I wince every time I get to that part of the scene. Luckily every other line in the film is delivered well, including a couple monologues that could have been really tacky in the wrong hands.
This must be some kind of milestone. One writer is singlehandedly responsible for the best and worst lines in a movie, yet little else in the film. 
I wonder if it would have been better without the whining.
But, Mr. Blue Sky, then it would have been out of character!
I nominate John Wayne in The Greatest Story Ever Told, a 1960s movie about the life of Jesus.
He played the bit part of the centurion who actually nailed Jesus to the cross. His one line in the movie came after Jesus died, and Wayne is shown in silhouette, with a backdrop of storm clouds gathering and lightning flashing. “Truly, this man was the Son of God.” came out as The Duke, nothing more, nothing less. It was laughingly bad.
And I found this, on the Turner Classic Movies site:
My submission is disqualified under the Shatner Rule, but I’d like to share it anyway.
In Roman Polaski’s “Tess,” there is a scene where Nastassja Kinski boards a train, walks over to someone and says, “I’ve come to tell you I killed him.” This line is so badly delivered that the theatre audience actually broke into laughter when it was spoken. Now that’s some bad acting.
In Fight Club when Edward Norton sees a male model in an ad, elbows Brad Pitt and says “Is that what a man looks like?” I dunno, it was just so forced? self conscious? clunky? I can’t quite put my finger on why that one line bugs me so.
I agree, it’s not an inherently bad line. You just have to imagine it being delivered by Sarah Michelle Geller with a perky smile, a shrug and a hair flip.
Not that she’s a good actress, but the single worst line I have ever heard is Denise Richards in The World is Not Enough (well, a whole lot of bad line deliveries, but this one especially): “Aren’t you forgetting something, Doctor?” It’s just awful.
“We can’t just leave her like this.”
– Matthew Modine, droning this line near the end of Full Metal Jacket
I love the X-Files movie, really I do; I’ve seen it 10 times in the past 3 years. But David Duchovny’s last lines make me cringe every time because it’s such an odd delivery. Why didn’t they do another take?
" No it isn’t. You were right to want to quit. You were right to want to leave me. You should get as far away from me as you can! I’m not going to watch you die, Scully, because of some hollow personal cause of mine. Go be a doctor. Go be a doctor while you still can."
Well, I’m not so sure about the “otherwise decent actor” bit, but…
George Lucas even says that one of his intentional recurring themes (and lines) in each movie is “I’ve got a baaaad feeling about this…”
That’s okay, in and of itself. For instance, Han Solo says it at times when they are going into a strange situation (and it works). Even in Phantom Menace, it’s use is appropriate – at the beginning, when the two Jedi are there for “negotiations” – and Obi Wan senses that things aren’t quite right.
BUT… it’s use annoys the hell out of me in ATOC, when Anakin says it.
The line should convey a sense of “hey, things seem okay, but they’re really not”. Instead, Anakin says it when he is TIED TO A POLE, and three dealy-looking monsters are being led out into the arena to EAT him and his friends…
“I’ve got a baaaad feeling about this…”
Thank you, Darth Obvious Boy
This is not the actor’s fault. That one was George Lucas’ fault for using it at that point in the script…
They probably did a bunch. Actors and directors often disagree on what the best take of a scene is, and the director may have liked that one more than a reading you’d have liked. You never know.
Nick Cage: “Put down the bunny!”
The Usual Suspects
Chazz Palminteri: “Now you talk to me, or that precious immunity they seem so fit to grant you won’t be worth the paper the contract put out on your life is printed on.”
I cringe every time I hear it. In a movie filled with sharp dialogue where does this piece of crap come from?
Well, I can’t find the actual quote, but it was more like “Yondah, in da tent of my faddah”, probably from the movie Taras Bulba. You also have to groan at his “I love you, Spahtahcus” line.
The worst for me was James Coburn saying “groovy” every five minutes in one of his old films.
The full line is usually rendered as “Yonda lies da castle of my fadda, da Caliph” and it’s from The Black Shield of Falworth (1954), one of Curtis’ first starring roles.
It’s Shatner-related, but Stephen Collins gets some of the dumber lines near the end of Star Trek: The Motion Picture including describing a human’s ability to “leap beyond logic” and “As much as you wanted the Enterprise, I want this!”
In the movie Soldier there was a doozy. A female character asks Russell what he intends to do to the soldiers attacking their base and the camera closes in on Russell in three leaps so he can deliver the line, “Kill them all”. Seriously cringe worthy footage. I don’t know if it’s so much the delivery(which was not great) as the camera moving in by three leaps which was supposed to build drama.