Behold the coffee-shop assistant. Some in high places say they serve the common man, but no one truly serves the public like the coffee-shop boy, or man or assistant, or whatever you choose to call him.

For 60 cents - the price of a black coffee without sugar - he is your servant. No tip, no service charge. Leave your nice clothes at home, he does not care if you are barefoot or wearing shoes of woven gold.

If you have some spare change, he owes you his attention. At the La Kopi coffee shop next to the Serangoon Central bus interchange, I have been working since 7.30am, wiping tables clear of fish bones, noodle gravy and substances that do not yet have a name.

At around 8.30am, the Two Angry Ladies come in. I take their orders.

I secretly wonder if they notice how sparkling clean their table is. I have wiped it with care and am proud.

"Mumble burble," mutters Tight Perm.

"Herp derp derp," wheezes Perm with Red Highlights.

"What?" I ask.

They let me have it.

"KOPI C SIEW TAI!" yells one, asking for coffee with evaporated milk, less sugar.

"TEH O PAN SAO! TAAH!" screams the other, in need of a tea, no milk, warm not hot, large.

Ow.

Asking a customer to repeat an order, it seems, is enough to trigger uncontrollable fits of rage in some people. I scamper away as fast as my feet can move, lest handbags and shoes rain down on me.

Perhaps they are brain surgeons who have stopped for a quick refreshment while rushing to an operating theatre where a life-saving procedure is desperately called for, I rationalise.

After two more people, teenagers, vent their spleen at me, I realise that some people see the coffee-shop assistant not as a human being but as a kind of punching bag, a convenient place to dispose of their emotional waste.

I suppose it comes with the territory. If your life is spent mopping up goo, you should not expect customers to genuflect in your presence. After all, if you could understand simple instructions, you should not be wiping tables for $5 a hour, they must think.

I tell the boss of the coffee shop, Mr Lee Seng Teck, 59, about how upset some people get when they discover that you do not read minds.
"Just say 'thank you'," he says cryptically, his hands a blur as he mixes drinks.

My trainer, Mr Derek Loy, 57, who has worked in coffee shops for almost a decade, murmurs his agreement before dashing away to deliver an order.

A thank you, I suppose, is verbal ju-jitsu that, if delivered with the right amount of insincerity, will either shame or infuriate the bad customer. Either outcome is good.

This silver lining in selling items that cost less than a dollar, it dawns on me, is that you can exercise sarcasm - or something stronger - on customers you do not like.

This morning, I am wearing cargo pants, with roomy pockets where I dump money. A good assistant carries a king's ransom in coins. Some customers prefer not to touch me and pay by dropping money on the table. The coins become slick with table grease, which is transferred to the fabric around my pockets.

I discovered the filthy-pants problem the day before but felt it was not a big deal. What was more disturbing was learning that wearing jeans, with their narrow pocket openings, was a bad idea. My hands, after inserting and removing money from the pocket again and again, become painfully chafed. A zippered pouch, also known as a bum bag, would make sense if I were to make this a career.

The money changes hands more than most people realise. It is standard practice that the assistant pays the boss as he is handed the drink. Then, the customer pays the assistant.

It is a brutally simple system that keeps assistants honest, as well as scrupulous in counting the coins the customers hand over. If the assistant messes up an order, he is out of pocket.

I end the day with no losses or gains in my money stash. I guess I was lucky that no one tried to shortchange me. If it does happen, it's usually by accident. Soft drinks, for example, can be $1.10 in one shop and $1.30 in the next. Some assume the lower amount when paying.

And true enough, a silver-haired woman grumbles when I ask for $1.30 for her can of green tea, saying that she paid $1.10 elsewhere. I smile sheepishly and say nothing.

La Kopi has a few regular customers, mostly residents who drop in on their way to or from work and a few retirees who come by to watch the daily wave of labour washing through the nearby bus interchange and MRT station.

Mr Loy knows who they are and once they exchange a nod, as if to say "the usual, my good man", he brings their drinks.

He likes being an assistant, he says. It is work you can leave behind when you clock out. No stress, he says. He likes La Kopi because it is a small unit, with 20 tables or so. Other coffee shops can have 50. It has just the right amount of activity for him.

I end my lunch shift at 2pm with a bowl of incredible mushroom pork noodles. I had been wiping up after the noodle shop's customers since 11.30am and felt it only fair to have a taste.

The next time you are in Serangoon Central Drive, drop by La Kopi at unit 01-87, Block 262. Say hi to Derek. Be nice to him. He is a good man. Then order a bowl of noodles and tell the man I sent you.