Arrogant cashier with a unprofessional attitude

Arrogant cashier. I am out of town and first time visiting the garage to exchange a 9kg gas cylinder. There was a long queue and when it was my turn the cashier asked to see the cylinder. I said that it was in the car. I was then forced to give up my place in the queue to fetch my cylinder. I fetched it and came back with it into the shop. When it was my turn again the cashier then barked at me to go and place the cylinder outside. I asked how I was supposed to know this as there are no signs explaining the process. The cashier then arrogantly asked me "how long I am going to have an attitude". This is totally unacceptable. The cashier should have displayed professionalism and rather have acknowledged that there is a gap in their process and that it would be addressed to make it clear to customers.