Oh my word, my hero.
My version of this was when I was just pregnant - maybe 7 or 8 weeks. Coping fine, not showing (or even telling people) but tired a lot of the time and clearly in a "no fucks to give" mode.
Anyone who commutes in London will know the Waterloo and City line - only two stops. So train arrives empty at Waterloo, everyone piles in, goes one stop to Bank and everyone piles out. Obviously at rush hour it's insanely busy and people are crammed in line sardines. The people who get on first obviously get the seats (sometimes they like to use their elbows) and then everyone else just squeezes in, standing room.
The reverse then is naturally true - the sardines standing in the middle get off first and then the people in the seats can exit.
A perfectly fit, healthy looking middle aged man had done the mad dash for a seat and nabbed one near the door. I was part of the sardine crowd standing in the middle between the two rows of seats. Didn't expect him to give up his seat but had (in my head) rolled my eyes at his aggressive effort to get one.
Train pulls into Bank station, and as the doors open he tries to stand up and push me and the woman standing next to me out the way so he can get out first. I didn't even think. Just slammed out my arm and grabbed the pole that was next to him so that my arm blocked him and said, "you got the luxury of a seat, now you have to wait until the rest of us are out of the way.". All he could do was collapse back into the seat as we all exited!
I got a few smiles and nods of appreciation!