This one time, at band camp, probably around 100.

I slept on the floor at the airport in Saigon in late 1972. The floor was wall to wall people. There had to be hundreds...

I stayed at a hostel with a couple dozen bunk beds in the same room. It was fine going to sleep but when I woke up the air was stale and smelled like bad breath and feet.

I'm already disqualified by @meepwa but I slept in a homeless shelter with 50 other people or so in the same room. And some of those people did not sleep through the night.

About 300 in a massive tent in Kuwait on my way to a deployment in Iraq. For an actual room, 40+ in the barracks after boot camp. Probably about that many in the reception barracks before boot camp.

Youth group trips I guess

I sleep in the woods fairly often, the world is a pretty big room.

I once joined reddit, but I don't think that's what you mean.

Canucks playoff round? 18,000 or so of us there.

Yes, it was a looong time ago.

Boarding school.

130 others!