A couple of examples from my game recently:
Married couple, maxed out romance level, sharing a meal and conversation with their daughter when one of them becomes enraged and gets a long term bitterness sentiment because her partner was cheating on her (by doing literally nothing else besides eating food and having a conversation with their offspring).
Toddler refuses potty training and becomes defiant literally just one time. Toddler then proceeds to a develop a long term grudge against one of their parents, that no amount of apology or positive activities/conversation will rectify. Sentiment still in place as the child is about to age up into a teen.
The only way I've been able to deal with both these scenarios is to use cheat codes to remove the sentiments in question.
Also the constant 'I'm so glad you don't think my llama jokes are old', and 'I feel like you just get me', in regards to Sims that have just introduced themselves & have maybe said two sentences to each other after that.
Anyone else getting weird, nonsensical sentiments in their game?
I had one of my Sims marry the Grim Reaper & now they have a lot of kids.