I live here. I've been a few times. I'm not doing it anymore.
It's a great cause and I suppose everyone ought to go once.
But spending a day riding (honestly, more often walking the bike and idling) with a half million bikes, doesn't turn out to be that much fun.
There's no shade, and often blisteringly hot on all the pavements, and no place to pee anywhere (or 25 porta johns for a half million). And bring cold water, you'll need it.
On my last run, while stopped (dead) on the Pentagon entrance ramp, just trying to get in, I had to pee so bad, I got off the bike and ran up the embankment and peed behind a billion watt electrical panel (seeing me do it, 50 guys did the same)(the girls were jealous but not that brave). And we never even got into the parking lot, until the ride started, and the crowd left, two by two, and sometime later we got in and rode through. When I got out of that mess, I went home, never to return
Lots of good riders, and lots of complete newbs, and you get to ride in close formation with them, all day, like a big accordion. Roll a bit, stop awhile, roll a bit, stop, repeat.
But don't let me talk you out of it. Experience it for yourself.
There's no need for everyone to start their engines. (about 2/3 are straight pipe hogs, so earplugs are good)
Some info on this year's ride.
https://wtop.com/dc/2018/12/rolling-thunder-comes-to-an-end-2019-will-be-last-ride/slide/1/And just so you know, DC has about 5,000 speed and light cameras that won't be turned off that day. (so slap a buddy's plate on for the day).
https://ddot.dc.gov/page/speed-cameras In summary, it's hot and crowded and noisy and not real riding, and you can't pee.
On the upside, the girl watching is some of the best I've ever seen. So there's that.
