Oh. I could make a list. But I'll keep it to just a few things.
First, the autonomous drinking of water. This action is nonsense, serves no purpose, no gameplay, and only takes up time and clutters the house (and inventories) with empty glasses. Even my Vampires drink water so I removed all of the sinks. It's a useless action and I want to strangle someone every time it happens in my game.
Second, the endless and insanity-inducing spamming of texts from strangers with the inability to completely turn off the phone. Why do we even have a "silence phone" option if it won't ignore all of those invasive popups? I also hate autonomous phone use. Just another reason for Sims to ignore each other.
Third, but most important - and this is a huge one- the emotion system. Why, why, oh why did they stray from the original Sims formula to favor emotions over the individuality and given traits of each Sim? I just... I can't. I will never understand this choice. This one bad decision managed to completely disrupt the integrity of the game and remains one of the main reasons for continuing controversy. RIP personalities.