How about speed, when Keanu finds the bomb on the bottom of the bus:
"Harry, there's enough C-4 on this thing to put a hole in the world!"
Unbelievably Bad Dialogue!
Oh yeah, and almost any line from Armageddon that is trying to be serious, while the other lines that are supposed to be somewhat cheeky are alright, like Owen Wilson saying "Scariest environment imaginable. That's all you had to say, scariest environment imaginable."
I don't know if anyone has said this, but what about Johnny Mneumonic? Dolph Lundgren says Halt Sinners! and puts his hand up to stop the vehicle (which ends up running him over!) I am not proud to say I paid to see that movie. Hell, I paid to see Action Jackson what a crappy movie!
When I said the Star Wars series, I meant the whole enchilada. Sorry. I'm a card-carrying member of the anti-SW lobby, although I do have something of a soft spot for Empire. But despite being the best of those films, it still has awful dialogue, as bad as any of the others.