This is similar to the question here: When in queue at the supermarket, how do I get my personal space? However this question is mainly focussed on somebody being in an area they should not be in the first place rather than standing too close in a queue. The person's rude/impatient behaviour is also a key feature.
I was recently in the supermarket, using the self-service checkout. I only had 2 items and was moving at a relatively quick pace (I would have been at the checkout for a maximum of 3 minutes).
There is a generally accepted 'queue area' at one end of the checkouts where but their arrangement doesn't make this immediately apparent and there was no other queue at the time.
A gentlemen made his way to the middle of the checkout area and stood very close to me as I was using the checkout. He only had one item but he occasionally made a 'huff' sound and seemed quite impatient. At one point he purposefully placed his item on the shelf of the checkout I was using - he did this very quickly, almost throwing it down. Very soon after the checkout next to me became available and he went over to that one, whipping his item with him and almost bumping into the lady who was leaving. Neither of us had said anything. I understand he was in a hurry but his behaviour was incredibly rude and fairly intimidating. He was very close to me and I felt quite uncomfortable when entering my pin number. (There's only so much shielding you can do when somebody is less than a metre away!)
My question is, is there anything at all I could have said to him to improve this situation and maybe point out that there is a usual queueing area.