Today I have been watching series six of CSI: NY for a review. It never ceases to amaze me how this show can get writers who are capable of good, twisty (if usually ludicrous) plots and yet cannot write dialogue to save their collective lives. More than once this afternoon I've thought, "Oh my goodness s/he actually just said that," and I'm only four episodes in.
(The only instance I can think of off the top of my head is where a couple of guys are chasing a street hustler who's been doing a bit of three-card monte. When they catch him, one guy says, "Looks like it's time to fold." GROAN)
Also, everything must be explained at least three times for slower audience members. I think at one point they managed to explain a plot detail six times in forty seconds.