I experienced explicit fatphobia on/around the train often enough that I would sometimes alter my schedule to avoid high volume times and times that coincided with the end of the school day, sometimes I would stand rather than sit so that other riders would feel like I was encroaching on "their" space less, and sometimes I would "rebel," and spread my stuff everywhere over multiple seats and put my sunglasses on - daring someone to say something to me. All of these tactics, in short, are exhausting for different reasons.
People are often surprised to hear that most of the instances of fat bashing I've experienced have been at the hands of women, most of them white and thin.
Being in or around shared public space really seems to bring out the bigotry in people. I imagine it has something to do with the anti-humanitarian, zero-sum mentality that capitalism teaches us - the more room you take up, the less room I have. I think it has to do with internalized sexism and women keeping other women down on behalf of patriarchy. I think it has to do with the "audacity" of a fat brown woman living in rapidly gentrifying San Francisco. All of this is exacerbated by the entitlement that permeates the culture of The City. So I came up with a theory: anywhere where my outer thigh has the potential of touching another person's outer thigh is likely not a safe place for me.