So a few weeks ago I was on television, doing a little comic "bit" about unfocused online haters, the climax of which involved me going into a diatribe wherein I angrily imagined one of them toiling away behind the counter of a fast food restaurant. And shortly after it aired I received tweets and comments from people complaining I was a snob: that I was in effect saying anyone who works in a burger bar is a scummy non-person; a grunting subservient ape-slave deserving nothing but open scorn and the occasional kick to the face, provided it's their birthday.

That hadn't been my intention, but I can see why some people interpreted it that way (thanks to some clumsy writing on my part, and an absent "qualifying" section, which got excised at the last minute). Anyway, it bugged me. It bugged me because although I've never worked in a fast-food restaurant, I did spend several years working as a shop assistant – and during that time I learned, as anyone who spends their week standing behind a counter quickly learns, that the worst kind of customers are the ones who think they're automatically superior to you just because you're serving them. The ones who pop into Debenhams and suddenly think they're Henry VIII inspecting the serfs.

You can tell a lot about a person by the way they treat waiters and shop assistants, especially when you are one. The majority of people are perfectly capable of interacting with retail staff without spitting on them or whipping their hides like dawdling cattle, but planet Earth still harbours more than its fair share of disappointments.

The first surprise is that when it comes to arrogant customers, class isn't as big a factor as you might assume. True, I'd occasionally get a stereotypical ex-public-schoolboy blurting requests in my direction as though addressing a programmable service droid, or openly scolding me as if I was a failing member of his personal waiting staff – but the most overtly boorish behaviour came courtesy of people who weren't posh at all, but seemed to want to increase their own social standing by treating the person serving them like scum.

Then there were the people for whom even basic civility was an alien concept. I vividly recall one guy who sloped in wearing a loose pair of tracksuit trousers, absentmindedly playing with his own bollocks as he entered. He stood at the counter, scanning the display behind me and obliviously juggling his goolies – at one point literally reaching inside to re-arrange his collection – and then wiped his nose with the back of his hand, sucked the slime off it, pointed at an item he was interested in and said: "Show me that." Moments later he started an argument about how much it cost, demanded a discount, and, when I refused, called me an arsehole and knocked a load of boxes off a shelf by the door as he left. Based on that one five-minute encounter, more than 17 years ago, I'd be prepared to bet that man is today either dead or in jail. And probably still playing with his nuts.

But incidents like that were few and far between, partly because there was one major difference between the shop I was working in and almost every other shop in the world: you were allowed to talk back to the customers. In fact a certain level of sweary piss-taking was actively encouraged. It gave the place character, made the working day more fun, and reminded the frazzled shopper, on autopilot after several hours on Oxford Street, that they were dealing with a fellow human being.

Everyone who works in a shop should be allowed to openly take the piss out of their customers. It's far more British than the strain of imported corporate civility-by-numbers that megachain staff are sometimes forced to recite: the robotic "How can I help you?" mantras that only really make sense in America, because they're so friendly they actually mean it. The words don't feel false in their mouths. If I ran a national burger franchise – which I don't – I'd make it a rule that no two customers can be greeted with precisely the same words, and that every third customer must be grossly insulted as a matter of course. Just to keep the atmosphere nice and lively. And to keep the staff laughing.

Yes, laughing staff. That's the other irritating assumption people make about working in shops, especially burger bars – that the job must be so dismal, every single employee shuffles about in a perpetual state of misery, actively welcoming death. That only the utterly desperate or dumb could possibly stick it out. These characteristics could apply to almost any job, of course. What I disliked most about working as a shop assistant wasn't the occasional snooty customer, or the shop, or the hours, but they way people reacted when I told them I was a shop assistant – their automatic assumption that I didn't enjoy it. I didn't particularly enjoy my life at the time, but I did enjoy the job. Not every day, not constantly – but I liked it more than I disliked it. Maybe I'm odd. Maybe I was lucky and had unusually entertaining co-workers. Or maybe there are far, far worse things you could do.

Like judging people.

Unless you're a judge.

In which case, continue.