I think it's disgusting that it seems to be socially acceptable to call someone out as fat on the basis that it's unhealthy and they clearly haven't noticed what size their body is or how unacceptable society finds their body shape.
It doesn't even work (if one's goal is to shame people into losing weight). I was labelled as fat when I was a child and teenager. I was probably a bit larger than average, maybe a stone or two overweight. Being ashamed of my body didn't help me to lose weight, in fact it led to negative emotions which helped me become 12 stone overweight.
I only lost some of that weight when I found an internal source of motivation. I realised that my health was possibly making it difficult for me to concieve, and that part of getting healthy (for me personally) was to lose weight. I got pregnant when I lost about half my target. :) I had known that I wanted to lose weight for ages, but I needed to be in a good frame of mind to set a goal and make progress towards it. Shaming me didn't produce that right mindset.
I find it difficult to talk about this. Because I personally found my weight was an indicator of how healthy and happy I was, I have to be careful not to extrapolate that to all people. Just because someone is large, it doesn't mean that they are unhealthy or unhappy. It certainly isn't my place (or that of some rude bloke in a bar) to tell someone that they ought to be unhappy or feel unhealthy. They know their bodies and are the best judge of that.
Excuses for verbal abuse I have heard, often relate to how unhealthy obesity is and how much fat people cost the NHS. This is rubbish. We don't go around verbally abusing people who smoke or drink even though these activities can be unhealthy. We don't verbally abuse those who do extreme sports and have accidents because they cost the NHS.
It isn't acceptable to abuse people or judge them based on their size. People in the street don't know whether I'm putting on weight, or whether I've made huge progress in losing it. I still look big to them (and now big and pregnant!). Whether I'm big and happy, or eager to lose weight, I should still be treated with respect for who I am at the moment.
I once saw a discussion about why gyms shouldn't provide large towels for larger customers because it would somehow normalise large people and the people should lose weight to fit the towels. Utter rubbish! Maybe they would use the gym more, and lose more weight if they were made to feel comfortable by having towels which they could wrap all the way around themselves.
Shame doesn't even work on the big scale of things. Our society idolises thin bodies in the media, but we are still meant to be in an obesity epidemic. If shame worked, we'd all be fitting into size 10s (or smaller).
For every women who heard a comment like that and used it as motivation to change, there are a whole bunch of others sitting at home reminded of why they don't want to go out in public to be judged by the critical (often male) gaze.