Probably an overhaul of baseline NPC behavior (behavior trees one day...), which I guess is a collection of mini-features but whatevs.
A lot of what I am thinking of is based on how monkey's acted in ss13 goonstation, getting really peeved if you sang around them, pickpocketing random people, maybe just deciding to shove someone over, being harder to wrangle in general too.
Station pets is another key part, a lot of them just sorta perform random-walks and thats kinda it for npc behavior. For example, cats could run under tables if a bomb (or otherwise loud startling sounds) go off. Having a cat knock an item off a table or a dog chase it's own tail would go a long way to make them seem like an actual animal and get the general playerbase actually caring about them.
