John didn't really do parties. The last one he'd went to ended in a fight and that had really been the only he'd attended. Parties were one of those normal teen things that were kind of tough to get into when you were on the run or bouncing around from foster homes while your Mom did time in a mental institution. So there was a bit of debate as to whether or not he should bother with the one here - but in the end he decided to check it out. He figured if nothing else this really wouldn't be a normal party either, given the whole apocalypse situation.
So John moved into the gym and found a nice wall. A good wall that he could lean up against and survey the event. Just because he showed up didn't automatically mean he would be the social butterfly. He figured showing up in and of itself was a good enough start.