there are loads of people in my gym who don't use padlocks so just put their stuff in a locker but don't lock it. I agree it's helpful to leave the door open to see which ones are free.
Agree the hair thing is gross though, but tbh if that's the worst thing you've seen so far in your changing rooms you're lucky.
Just a selection of annoying things I've witnessed are:
people filming each other doing tiktoks
having private conversations (to each other and/or over the phone, including
giving out their credit card details) and then glaring at you for having the temerity to use the hairdryers so they can't be heard,
using the (small!) changing room floor to do their stretches (and, again, glaring at you when you step over them to get to your locker)
blow drying their pubes
bringing kids in outside of kid hours, including boys who are far too old to be in the women's changing rooms
saying 'yeah come in' to the male cleaning staff without checking with anyone else, including those in the showers.
And that's just the changing rooms, don't get me started on annoying gym/pool behaviour!