I know what you are talking about, but I try not to think about it too much. First of all, you have no way of knowing for sure that they are being passive aggressive, or just trying to be polite but coming off awkwardly. I hate when people make assumptions on how I must be feeling, so I try not to make assumptions about them. Maybe they got some bad news that day, are struggling with something I’m unaware of, etc.
If I do detect some sort of aggression, I just try to complete my part of the transaction as quickly as possible and be on my way. Maybe they are irritated, but I don’t need to hang around to find out, and digging into it isn’t going to help either of us.