I don't believe there is any line bad enough that a good actor can't save.
If a scene isn't well written they'll drop your neckline to fill the void.
My experience is, I do a table reading, and it's literally like it's written in colossal neon lights what's wrong with the screenplay.
The problems I have with a flawed script are always revealed in the editing room.
A lot of times, scripts are written so the character is all one way. Even with 'Bringing Out the Dead,' the character was written a little more generic.
With some writers, the script looks beautiful on the page, but nobody actually speaks like that.
Finding a good script is really difficult and the scariest thing of all is when they say about a script that's not right, "we will fix it.." It's like before you get on the Titanic and you see a big hole. In process, it's too late.
You can't fix a bad script after you start shooting. The problems on the page only get bigger as they move to the big screen.
I love it when actors come to you with a problem and you have to listen. You'd like them to just get on with it, but it often means that there's a problem with the script.
For me, most comedy scripts fail in the mechanical playing-out of the setup. They'll pay lip service to a moral lesson or a psychological progression.
If it's a terrible script, it's a terrible bore.
I find that dialogue is bad in most scripts. I just think there are very few writers that can capture the natural way people talk.