Buses, vans and subway trains
Jan de Bont's Speed (1994) is a pretty stock-standard action movie. It has a pretty clever plot. It involves Keanu Reeves and a bus. You've probably seen it. What you may not have noticed, however, is the worst throwaway line in movie history.
(And that's saying something, considering Speed contains such dialogue gems as "It's cans, it's okay, it's cans".)
There's a moment toward the finale of the film where an extra spouts a line of dialogue. There's no real reason he has to say anything, but he does anyway. I can picture the editing room: the scene is cut, the audio is laid in, and the director and editor are arguing over whether a soundbite needs to be overlaid as the extra does his thing. The correct answer is "no". The answer they chose to go with is "sure, lets see if we can dig up something that seems relevant enough", followed with the addendum "but really isn't".
They've clearly rifled through all of their available chunks of pre-recorded dialogue, hoping to find a sound clip that fit. And when I say "fit", I mean "with a shoehorn and vaseline".
Keanu Reeves and Sandra Bullock ride the remains of half a subway carriage as it roosts through the pavement of an unfinished railway station and skids down three or four blocks of a Los Angeles street -- on its side -- before coming to rest against a blue minivan. The driver of the van climbs out, bewildered, staring at the bizarre sight of an upturned and halved railway train on the roadway. And he says:
"I can't believe he hit my van."
No one would say this. A more appropriate outburst would be "HOLY SHIT, A RAILWAY TRAIN", or "JESUS, THAT WAS LUCKY, I'M STILL ALIVE".
This may be the worst line since "You're the man now, dog", and I think Speed is all the better for it.