I don't tend to hold personal grudges but I hold the deepest ones about TV plots. I realised, when it came on my shuffle, that I'm still furious the choice of "all along the watchtower" in Battlestar Galactica didn't lead them to end up in the late 60s or early 70s on our earth

I have many of them. The fact that buffy's power sharing spell only asked consent from the slayers she was in contact with but for all the others, she was basically doing what the watcher's council did to the original slayer! DAMMIT BUFFY. (17 years and counting, this grudge)

Feel free to add your TV plot grudges!

Another: the fact that they turned David Tennant's Doctor into a weird shrivelled Dobby creature that did nothing and wasted all that Master/Doctor finale energy and glory!

All of Lost, basically. I stopped watching mid first season thinking "they don't have an endgame, do they?". VINDICATED.