Bad writing for film and television really irks me because of how avoidable it is. I'm not talking about mediocre or lackluster writing, but the actual bad writing.
TV shows and movies are tremendously expensive to make. Every part of it costs a fortune except for one: the writing. Even if a studio or production company was paying for a whole team of writers to work full time it's still only a fraction of the cost of paying film crews, actors, editors, and VFX artists.
Given the relatively lower expense, relative lack of time constraints, and enormous importance of the script to the overall quality of the product it absolutely boggles my mind that production companies consistently fuck up the writing process.