No.

It’s the first word many children learn — and often with unexpected and undesired results for their parents. Nobody is entertained for long by a toddler empowered beyond his station by knowing how to say “No!” to his parents’ directions.

But “no” is also a word that, quite frankly, is heard far too little in society as a whole. No is to those who believe they’re entitled to the fruits of others’ labors as kryptonite is to Superman. No is to the creeping rudeness in society as the moat is to the castle. No is to arrogant presumption what the guard dog is to the intruder.

But still, it’s a word many of us find ourselves afraid to use — whether to spoiled children or arrogant politicians, to insolent teenagers or rude telemarketers.

During the weekend, a clerk at a Suffolk convenience store became something of a local cult hero for wielding this word with such authority that it caused a would-be robber to flee the business empty-handed.

The unidentified man entered the business with a piece of clothing over his face. He did not display a weapon, but he asked the clerk to come to him at the register, where one must assume he intended to paw through the drawer for a few ones, fives and 10s.

But “No” stopped him in his tracks. In fact, “No” had the power to send him running.

Now, don’t get us wrong. We recognize that this could have been a dangerous play on the part of the store clerk, and we tend to agree with the common advice to just give robbers what they ask for, cooperate to the best of one’s ability and do what’s necessary to get them on their way.

The police wind up finding many of these folks, even when the surveillance cameras return images that look like they were shot with a Fisher-Price “My First Convenience Store Security Setup” camera.

We especially urge cooperation when there’s evidence or the suggestion of a weapon in play. When the choices are between cooperating or getting shot, it’s often a better choice to cooperate now and live to press charges later.

But still, we join many others in Suffolk in tipping our hats to the clerk who just said, “No.” That’s the person we need to get on the phone when the telemarketers won’t stop calling.