I'd forget it was happening until the morning of the party, when I'd be reminded by a phone call from my ISTJ friend. He wouldn't be calling specifically to remind me, but for advice and instructions on what he should wear and what he should bring, and to quiz me on exactly who would be going, the format and schedule of the party and what he should expect. I'd answer that I've no idea about any of the above, and he'd grumble and ask me what I was wearing. I'd respond by describing my current attire, being facetious, but he'd not realize and think I was serious.
I'd turn up at the party wearing something clean and classic, not showy or flashy, but smart and elegant. I'd probably be about half an hour late, at least. Not deliberately, but just because I got distracted en route by something popping into my head that I figured I'd best take care of before I forgot, and then several sidetracks later, I'd be back en route.
ISTJ would be mad at me, because he arrived long before me and didn't know anyone and didn't have anyone to introduce him, so he stood around like a lemon. He'd also be mad at me because I was dressed smartly, whilst he was wearing something similar to what I had been when he phoned me - a pair of scruffy jeans and a plain t-shirt, unironed. I'd pat him on the arm and chuckle and say something that put his attire in a new light to everyone and made him feel jolly stylish, and then I'd go into the building.
I'd want to take a quick tour around the premises, so I know the lay of the land and what sort of crowd we've got here, and in the process I'd be stopped by lots of people I know and introduced to lots of people I didn't know. I'd get sidetracked a heck of a lot, and it'd probably take the best part of an hour for me to finish my tour, if I was really determined. But before I began it, I'd get myself a drink - if you walk around at a party without a drink, people think you're a roadie or a bouncer or something and nobody talks to you. I wouldn't want an alcoholic one though, not yet.
I'd start on the alcohol after about two hours had elapsed, once I knew everyone's name (but probably forget it before I talk to them again) and had a general idea of what kind of person they were. That way, I'm less likely to make serious gaffes when drunk. At this point, I cease to have any control or even desire to have control, over what happens and where I am/what I do/who I talk to. I become the ball in the pinball machine, pinging faster and scoring higher as the night goes on.
When everything's finished and most people have gone home, I'm the one standing, leaning against the wall with my hair messed up out of its original style by all the ruffling it's received both by me scratching my own head whilst thinking of a reply (a habit of mine) and other people ruffling it in that "Oh, youuuu!!" way that they do when someone gets away with a cheeky jibe. I'm talking to another couple of people (we only met each other that evening), and we've barely noticed that the music stopped and the lights came on. We continue to talk as we occasionally have to move our feet for the caretakers' brooms, and move aside absently for the occasional amp-carrying roadie.
We don't want to stop partying, so we drunkenly hoof it to some mutually, spontaneously agreed destination, such as a nightclub if there are any still open, or one of our homes or the home of someone else one of us knows that's sure to welcome company at any time. Either way, we all end up crashing out on some strange floor somewhere, and manage to, between us, procure coffee and bacon sandwiches the following morning after being rudely awakened by a vacuum cleaner to the head. Tsk. Cleaners should know to check behind chairs for random sleeping people!!
Then it's a walk back to the car, wherever I left it, and a bleary drive home to relieve the babysitters.
That's how it usually goes, anyway.