How loud is loud?

Seems like a rhetorical question, but I'm curious what other folks think is "ok, now that's loud"

For me, if something's hitting 100dB as measured from where I'm seated while listening, and not just for a brief moments, but with some regularity, that's loud.

I used to listen at higher average volume than I do these days. Typically, I'm finding that at the right volume, the recording is more nuanced then when it's running full throttle.

If I'm not mistaken, the late Peter Walker observed that every recording has it's one correct or optimum playback level. I think generally he was correct, though once we are willing to forge optimum there's a range of acceptable.
My average listening level is in the upper 50's to low 60's. Rarely do I get it up into the 70's. So, loud for me is into the 70's and up. Depends on the room, the system, and the listeners threshold levels.
Rarely is the time I can listen to anything loud. I don't go to conerts hardly anymore due to it being so loud.

It's little girls with guitars for me :-)

All the best,
My average is between 85db - 95db at my listening chair for hours with out any fatigue.
Check with the local police department since they are governed by each town ordinance which spells out in db's what is loud and when it is loud. Then get a sound meter and have someone go outside when you are listening at levels you think are okay. Then, call the police and report yourself since I am sure you want to be a good citizen first. Yes, I have had the police come calling. No, they did not come with a sound meter, so they were confused when I mentioned they had no way of really knowing what loud is. Yes, they felt I was a wise guy, but did not arrest me.