Just thought of one that really grates on my nerves. The "know-it-all/kid is the smartest person in the room'" trope.
In Heartland, there was this character that had become really annoying in the way she was written. First was in the way she was written in, in the first place (Character's parents aren't currently home, so she gets to stay the summer at the farm.) Then the writers had given her facts and figures to randomly quote, even if they're topics she has no experience in. This had been done so often that it started becoming a character trait of randomly deploying facts and figures. And always when there are more experienced adults in the room. The one thing that made me roll my eyes was when one of the characters was pregnant and about to have their baby, and the know-it-all who's probably in her early teens with no experience is suddenly the expert in pregnancy trumping characters 3 times her age who are in the room with her. I couldn't wait for her character to be written out of the show, and it was a relief when she had. What an awfully written character.