I have, I sympathise! Had a very funny encounter on a bus once on the way back from a scan at King's. Unsurprisingly, there was another pregnant woman who got on at the King's stop. Now I was 6 months along or so, but she was super-pregnant - 10 days overdue as it turned out and looking like a balloon on legs as you do at that stage. No-one stood up for her, so I asked someone to move for her, which they did. When a seat finally became free I did sit down, and the woman in the seat behind me tapped me on the shoulder and said 'I'd have stood up for you, but I've got a bad back'. Then the woman next to me then said 'I'd have stood up for you, but I've got all these bags'. Then the woman in front said 'I'd have stood up, but I can't get out of my seat' and glared at the woman (whom I think didn't speak English) next to her! By this time I was really embarrassed, especially as I didn't really need a seat that day for a short journey and was feelign fine. But afterwards I laughed my socks off.