It's good that you make the extra effort, but it's not like these people are waiters that make their living from tips. I work a lot too and sometimes get frustrated with customers, but that doesn't give me license to treat them like crap.
My job can be pretty stressful too, but I rarely have to deal with a washroom stall covered in filth from the most disturbing case of explosive diarrhea ever.
Likewise I'm not usually expected to escort out a distraught, screaming homeless person who is having a psychotic episode in the middle of a busy convention center.
Hakuna Matata.
Just assume someone has dealt with something like that or worse and it gets easier to be nice to them, even when they're behaving like right old pricks.