But what really got me was a comment (yup, I read the comments section - many of them are horrendous):
I am very conscious of this issue on the bus, and I make an effort to take up as little room as I can – I put my bag on the ground between my feet when standing, or on my lap when sitting. I move over as close to the edge as I can, and I keep an awareness of my surroundings. I move to areas where I have more room to get out of the way and I genuinely think that my girth does not impact negatively on those around me in most cases.
...realise that some of us know perfectly well how large we are, and that we attempt to be as considerate as possible.
I'm not against consideration in public spaces. I've squashed up to help other people on, or given up seats on trains to those with clear difficulty standing (I have a level of difficulty myself, but I usually found I could sit on the steps with no problems). I'm wary of judging how people are positioned, because I don't know the reasons for this, but I have no doubt that some are just being plain inconsiderate.
But it's much more than that. I've recognised this tendency in myself, and in others, to apologise for your size, to make yourself as small as possible. Clearly if a seat is too small for the people sitting on it, in the short term both are going to be in some discomfort and, all else being equal, it's up to both of them to absorb some of that discomfort - but it should be about just that, a mutual effort to deal with a problematic situation, not the onus being on one to not inconvenience the other. But I've myself as small as possible to try and prove I don't need the whole seat, even when there is plenty of room. I've been reluctant to spread myself out on long haul flights when there's been a vacant seat next to me, in case someone thinks I can't fit in the seat.
Consideration for other passengers is one thing, but this isn't about that. It's entirely about self worth and whether we feel we have the right to expect public transport that accomodates the size and shape of our bodies. Or our disabilities. Or doesn't take the average male body as the default. Maybe if those who feel squashed on bus seats could recognise it as a design issue, and become allies, they'd achieve a whole lot more.