I often lock open the First Class internal doors on Ascot to Guildford trains due to the high prevalence of anti-social behaviour on the line.
They constantly changed it. It was always in use when it was 450+458 operation pre 2014, and then it was exclusively standard only 456s 2014-2016, and
then it became 456s and
declassified 450s.
After a couple of years the 456s went, and 450s supposedly became reclassified again but some guards continued to push the green button and announce it was for standard class use, whereas others didn't. And then when they split the service, I think they declassified it again for Ascot to Aldershot, but kept it classified for Guildford to Farnham.
And on top of all that, you had Waterloo to Farnham via Staines trains, which were classified Waterloo to Ascot and declassified Ascot to Farnham all the while Reading trains had first class and Guildford 450s didn't, then became declassified the whole route, then became declassified Waterloo to Ascot and
sometimes classified Ascot to Farnham depending on what guard you got, and then entirely declassified again.
Very, very confusing, and the classification in timetables wasn't always accurate or kept up with changes.
Back in late 2022, I was unfortunate enough to be on an Ascot Aldershot service approaching Frimley when the female guard was sexually harassed by a group of men. She asked for help over the tannoy. Some people are absolutely awful.
The local trouble-makers (and that's putting it politely) have figured out what the little green buttons above the doors do, and have made a habit of taking over the First Class compartments and locking themselves in there so they can smoke / vape / commit vandalism (delete as appropriate) in private.
On my way back from Portsmouth to Cardiff several weeks ago, two very loud women with a baby in pram and another small child entered the declassified first area (I had the right hand side table in the back row, an off duty GWR staff member had the left hand side one) spread over the two tables in the front row.
Once the off duty staff member (whose jackets and bags were all over the seat btw, so that's the last time I listen to a GWR guard who tells me not to put my luggage on the seat) alighted, they parked the buggy in the aisle, and forced the internal doors closed.
They were rather loud and obnoxious, but even though the main 3+2 standard class was full and standing, these selfish women closing the doors that said "First Class" and completely blocked the entrance to the area with the buggy anyway, did mean no one else tried to enter, and I had a table to myself the whole four hour journey. So I did sort of win from that.