But by telling her that she has invaded my personal space I am basically telling her to stand up. There is no middle ground, she was unable to sit AND not invade my space. I find it rude... or at least uncomfortable, to demand that a person stand. I know it's a sensitive topic, but I'm actually asking how to best be polite to them, and sensitive to the fact that they might not have chosen this condition, I am not trying to marginalise them or put them down. After all, I could have stood and let her have the seat without her feeling uncomfortable (because I'm sure she didn't feel great either). And I don't think she is less deserving of a seat than me, even if I am pregnant, because at this stage I am quite capable of standing.