I've noticed several times, especially at parties, that sims just can't seem to sit properly in their chairs.
They'll stand with food and scream at the chair, then dump the food or sit down and eat.
It took a while to figure out it was because another sim was walking by behind the chair.
This isn't so much a critical issue until I tried to take another sim to the bistro. For whatever reason sim 1 would exit the bistro with food and wait, sim 2 would eventually come out and they would go to a table. Sim 1 would try to sit but sim 2 walks behind his chair and stands there (no comment about this catastrophe at this time), eventually sim 1 gives up and dumps his food and walks off and sulks while sim 2 sits and eats.
just ignore the massive floor space requirements of chairs for the love of god.
otherwise ensure that other sims aren't always so oblivious to what other sims are doing. as in if they are talking, they could move aside as part of the sitting sim's action of sitting. it forces other sims to move but doesn't interrupt what they are doing.
Forum needs a Sympathy option to add to disagree (automatic), Agree (after finding proof of statement elsewhere), Like (not sure what this is for other than sympathy comments to OPs that done a bad), and LOL (at oblivious people posting comments fishing for sympathy).