Giving up your seat on the tube.

I have never hesitated to give up my seat for someone who needs it more on the tube. If it looks like you need it more than me, TAKE IT. You don't even need to ask! However yesterday this heavily pregnant woman stood infront of me and literally almost poked me with her belly. I looked up and she gave me a patronising look. Anyway I stood up immediately to allow her to sit down and she didn't even say thank you. What the fuck? Is that where we are now? Disclaimer, I was not sat in the priority seat. I'm still baffled and annoyed by this. It takes nothing to say thank you and you should never push your protruding belly onto people.