She was a slight, youngish woman, dressed in jeans and a jumper, waiting for the bus with her shopping. Bored at the long wait, she was busy having a good old natter to a friend via her mobile phone.

"Don't be ridiculous," she laughed. "We all scream at our children - they can be right brats when they want to be. And they always know when to get at you, when you're at your most stressed. "Feel guilty? You must be joking. Sure it's good for them. We take turns at it in our house.

"No, no, I'm telling you, the neighbours won't mind . . . . Anybody who has children knows what it's like."

Rare honesty in a parent, I thought, a little nervously. "There I was, I didn't have to go to work 'til noon, I was getting ready to clean the house, when he rang. He'd forgotten his train pass and wanted me to go down to the station to give it to him. "I was raging. I hopped in the car, drove down, rolled down the window and flung it at him. `Don't you ever do that to me again,' I told him. I phoned him this afternoon from work and I warned him: `You're grounded forever, don't do that again.' "No, it's not too harsh. You've got to keep them from stressing you.

"The other thing I use is: `Don't talk to me, don't whinge, it's that time of the month.' That's all I have to say and they know it's time to back off."

AT THIS STAGE, I was torn between edging rapidly away from scary Mom, or grabbing the phone to tell her friend: "She's wrong. Sure, we all scream at our kids at times, say and do things we regret - but listen to your guilt. It's telling you that screaming at your kids all the time isn't good, for them or you."

It's one thing to throw the head, even on a fairly regular basis - quite another to elevate roaring and shouting to a parenting principle.

Or does it make any difference? I suppose the children on the receiving end can't really tell.

At any rate, the mammy at the bus stop provoked an examination of conscience - and a story for the kids: you see, there are parents meaner than me. Of course, maybe she was all talk, and soft-centred when it came to action. But you had to feel sorry for her kids.

Without knowing it, parents are watching other parents a lot of the time, seeing how other people handle the business of bringing up baby. Often we learn how not to do things, as well as better ways of behaving. It's also good (if somewhat mean-spirited) to know that other people have troubles worse than your own: studying the advice pages of parents' magazines can be quite cheering, as you read about problems you didn't even know existed.

While parents talk to each other about their families to a degree which would shock most children, they seldom criticise other people's parenting behaviour out loud: this is treacherous territory, for even the most easygoing of us has deeprooted feelings about the right and wrong way to raise kids.

Parents with a positive, modern, liberal approach to child-rearing would be horrified by the "keep kids in their place" school of thought; parents with a more robust, decisive, controlling approach undoubtedly think this weak-kneed and wet.

There are situations when you long to speak your mind. Which of us has not twitched to tell the parent of a badly behaved three-year-old to get a grip and stop them disrupting all about them - instead of gritting our teeth and murmuring "gosh, you're so patient".

Or who hasn't wanted to leap to the defence of a child who is being ill-treated by a parent in public? One friend recalls an incident in a restaurant in which an overbearing father reduced the tables around him to an unhappy silence as he openly berated his seemingly inoffensive 10-year-old son: "You always cause trouble, why can't you be like your brother . . . You're stupid . . ." etc.

Should somebody have said something to the father? If you see a parent cuffing a two-year-old around the head in public, as I did recently in McDonald's, should you speak up? Most of us do what comes naturally - which is to keep out of other people's business, even if we feel badly for a child.

AT THE VERY LEAST, this kind of incident is useful in making us examine our own parental behaviour: sometimes the only difference between those parents and us is their unselfconsciousness about behaving like this in public.

Quite a few of us turn from street angels into house-devil parents. It can be a corrective shock to realise that, from our children's perspective, we sound, we are, just like those "bad" parents.

Yes, you can learn a lot just by watching. But watch out - another parent might be watching you.