Oh mi God FishyFishy.... I can't believe that people would say that to you! Hold on, yeah I can, but still.... oh dear I feel so much for you, how people can be so rude to someone they don't know. And someone that they have no idea of the situation, the circumstances..... its so pathetic it is literally making me sick with anger right now.
If I were you and I'd heard someone the bus driver say that, I'd take his name, the bus number the route you were on and report him because I don't think anyone can say that let alone a bus driver. They must answer to someone.
I'm tall too and I have always been really skinny, I do not and nor have I ever had an eating disorder but when I got pregnant people naturally assumed I was a crack addict or a heroin addict.... that was hard to deal with. I wasnt drinking, smoking or even having a class of coke while I was pregnant with my daughter.

Now I have my little girl and the shops we frequent are sort of used to us now, of course at first we got stares, but now people now we are for real, we a married couple with a daughter we love very much. And we survived peoples accusations and nasty snide remarks and I'm sure I'll hear even more when I get pregnant again and have a big belly and a toddler.... its sad but its true.

But as long as we know there are others who go through the same **** and we just adopt the personality of 'you cant judge us by age, judge us by our parenting skill once we have the kid' like everybody else.

Good luck..... and I do ramble on, I'm sorry.