i can relate too and it pisses me off to no end! i haven't gotten it in a few months, but it happens several times a year. the last time i went to take a test for a county job, while i was waiting in line to check in it's finally my turn, i give her my ID and the conversation goes like this:
worker: "no babies today, ok?"
me: "excuse me?"
worker: "are you pregnant?"
me: "uh no, i'm just fat"
worker: "oh, my bad"
seriously, fuck off. i've found that most people then act like what they just said didn't offend me at all and seem like they have no shame. i almost want to tell them "oh, you mean when am i due to lose this weight??". it goes both ways too, even when i was pregnant i'd have people go on and on about how huge i was, if i was having twins, etc. and that didn't make me feel any better either.
sorry for the long rant, this is just something that i'm all too familiar with. i do wish i had more motivation to get up and do something about it though because it pisses me off so much. even so, people just need to shut the hell up already.