The Core. Definitely bad writing as well as bad direction and bad science. It's up there in the so-bad-it's-good category. Jupiter Rising. Some absolute clangers in that: "The bees always know" "But I like dogs"
Hollyoaks, a british soap. Even for a soap, it's terrible. Someone dies or ends up in hospital every other episode, psychopaths are kidnapping or killing every other day. Plot lines are always convoluted and almost never make sense, there's no reason for me to care about any of the characters; the whole thing is just one big clusterfuck. Lost was just a constant headache. And now that I'm having a think, probably the worst writing in a movie I've ever seen is a 1999 crapfest called Silicon Towers. *shudders*
Dr. Who has gotten bad enough I stopped watching it. But if you really want to experience some bad SF writing, look to films like Battle Beyond the Stars.
I have a friend who's a diehard fan of Dr. Who. He feels pretty much the same way. I'm not personally a fan, so I can't quite understand.
I suppose the directing could have had something to do with it, but over all I feel the artistic aspects, such as the acting, etc. were fine. The story was lacking in much depth. I understand that it was a coming of age story, but it droned on and on and seemed more like toast than meat.