‘Function’ can also be used to describe a large social event, usually where you’ve bought a ticket for a fundraiser or you’re attending a graduation or the opening of an art gallery.
This is not the same as ‘social functioning’ but you can definitely gauge a person’s social functioning abilities at a social function.
Usually, social functions are comprised of a bunch of grown-ups who get ‘dressed up’, there’s crappy wine, cold appetizers and mingling with small-talkin’ strangers and acquaintances. Sometimes there’s a good band. Not a big fan myself, would rather be dancing my ass off in a club, but you know, ya gotta put in an appearance or everyone might think you’re dead, or a really annoying figment of their imagination.