Doesn’t compare to the wonderful stories here, but for me it was going to an Indy car race at Laguna Seca in the late 80s with my next door neighbor and a few of his friends. We took his Suburban, and knowing we’d be stuck in traffic for hours on end, we put a big tub of ice and a keg of beer in the back.
When traffic stopped up, we started handing out free beers to all the cars around us. Instant road party. All five of us were pretty outgoing guys anyway. About three hours of moving the vehicles every ten minutes or so, and hanging out laughing and swapping stories of races past. I think we had about 50 people in all drinking with us.

I’ve had great times at tracks - some with that same bunch of guys. But for some reason nothing beat just turning what could have been the dullest day in to a lot of fun for a bunch of strangers.