During my shop last week, I happened to find myself waiting behind a lady who was crouched towards the bottom shelf. She was there a while before she looked up and realised I was waiting and was very apologetic to which I tried to tell her not to be. Even though I had done nothing wrong, I felt bad because after she had been apologetic, she never took anything and I felt as though I had rushed her in some way. Then when I arrived at the tills I saw a 'distance marker' free at a till so I went and stood on it only to hear from behind 'excuse me, I am queuing for this till' to which I responded politely and apologetically that I hadn't seen her waiting there (she was halfway down an aisle and leaving more of a gap than the markers suggest for some reason).
In both of those instances, there was no tutting from anyone, no harsh words, no dirty looks. Everyone is feeling it at the moment, everyone is living with that worry about themselves and about friends and family so now, more than ever, is the time to be considerate and patient of others. And if you do want to nip in to grab something from a shelf and someone is in your way, just politely ask them if you can sneak in to get whatever it is - amazingly you will find that the vast majority of people will happily comply and will do so with a nice smile