Nigerians.
This is not me being racist, this is just observed through my own 3 years working in a shop where I have had to photocopy alot of documentation for people from other countries.
I can say that, without a doubt, there has only been a handful of nigerians I have served in the shop that has not been, on some level, rude. From jumping the queue, to demanding tippex/scissors/sellotape, to not saying please or thank you, to pushing their papers at me, having kids running riot in the shop, calling me a stupid girl, tutting at me, pushing other customers bags off the counter because they need to fill out a form, taking off their shoes in the shop and demanding I fetch them a chair to use while their fax goes through... and so on.
Apparently it is a cultural thing, I have a friend whose boyfriend is Nigerian, and he said they have a very abrupt and demanding culture. It just clashes alot with ours!