Why do people get so annoyed at the smallest inconvenience at a place of business

I was at the gas station getting a crappy sandwich. There was only one person working and she was a senior citizen. She was a little slow to count out the money of the first person in line. The second person was huffing and puffing and turned to me and said can you believe this. I responded with “It’s not a big deal chill out sir”. Got pissed at my response. They’re card was declined. I let out a ha and they stormed out. Do you have any similar situations. I’m sure a lot of us have