You did not breach any etiquette, but I also think that the bankers were maybe just trying not to be rude to you by looking. I EBF for the first 6 months and now I've done it, it is easy to get on your high horse and say "what's the problem folks", but I forget that before I had DS and my sister breastfed, it didn't make me uncomfortable, but I had no idea where to look, although I had no issue with it whatsoever.
I think the bankers just didn't have much experience of someone breastfeeding, so didn't really know how to react for your sake.
It's a shame that more breastfeeding isn't done more widely publicly in this country as people are only going to learn how to react if they see this happening often.
Before I breastfed, my DH would prob have been a bit embarrassed at someone breastfeeding (again, not through any issue of breastfeeding), but only cause he knew nothing about it then. He wouldn't bat an eyelid now.
I recently bought a car and it took a long time to negotiate and to get everything sorted, so I ended up breastfeeding in front to the car salesman. He was great, didn't bat an eyelid and I got a great deal on the car!
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Don't be worried about breast feeding in public. If people are a bit funny, it is probably just that they are a bit unsure what to do, but I bet the next time they see it, they will deal with it a bit better.