 I'm curvy, but petite. I'm 5'1" and about a size 6-8 US with most of my weight being in my butt and boobs (I'm a 30F so big boobs, small frame). 

At least once/month, a woman offers me a seat on the subway - crowed, not crowed, doesn't matter. ALWAYS slim/skinny women. Sometimes they watch me walk in, stare at my stomach area then immediately get up, wave me over loudly "would you like my seat?!" and then become insistent when I say no, I'm fine. At first I used to say, "No thanks - I'm fine!" and now I just say "No" bluntly and look away. They still offer. Sometimes they'll be sitting for 2-3 stops without looking at me, then when they *do* look they immediately panic and offer me their seat while standing and making room for me to sit. "Please, please take my seat!", etc.

I wear a typical "Canada Goose" style jacket with a waist belt cinched in to emphasize my smaller waist. My sister even joked "Now people will stop offering you seats on the subway!"

Again - I DO NOT LOOK PREGNANT. People often point out how small my waist is. 

It happened this morning. Got on subway, stood for 2 stops, woman looks up and then loudly asks me if I'd like to take her seat while getting up and moving away, waving me to sit. I said "Nope" and looked away. I could see people staring at me like, "Well, that was a bit rude...!" (to me because I said no and looked away!)

My husband, at this point, is pretty angry that this keeps happening because he knows it hurts and he can see in my face that I'm embarrassed. Today he 'joked' that next time he's going to call them out and embarrass them, but I told him I don't need defending and can stand up for myself.

But WIBTA for calling them out and embarrassing them back? What do I even say to that?? "No thanks - and I'm not pregnant...." He thinks that would be enough as they'd just shut up or apologize but I think they'd just double down and deny that's why they were offering. But I'm entirely able-bodied, don't have a cane, I'm young (37 but easily pass for mid-late 20's), I stand and don't complain, etc. There were even other women standing around me today - all small framed/slim. I didn't see her jump to offer any of them seats.