Teenagers aren't all the same. It's tempting to pretend they are, especially when they've made you cross.
If they won't reply to your frantic texts, or you can't see the floor in their room, or they argue the detail of every tiny thing you ask them to do, you can grit your teeth, and think, "Oh, teenagers."
But while it's a sort of comforting fiction that wild moods, reckless behaviour and, on occasion, startling rudeness are common to anyone who's aged between 13 and 18, this isn't really true.
Some parents sail through their children's teenage years without a ruffle of disagreement. Really. "We just get on," says one mum I know. She's a very nice woman. (Perhaps that's where I've been going wrong.)
Others have non-stop arguments - shouting, broken plates, slammed doors. The arguments are usually worse with the first-born, because the eldest pushes out the boundaries while parents are struggling to reinforce them with barbed wire. Younger siblings just don't have to fight so hard.
"You let them do so much more than I was allowed to do," said my eldest one evening when his brother and sister were both out.
"No, I don't," I said.
But secretly I thought he was probably right.
What makes it even harder to generalise about teenagers is that you can't really compare a 13-year-old to an 18-year-old. (Unless you're talking about the number of hours a young male wants to spend playing computer games. In that respect, a 12-year-old seems startlingly similar to a 22-year-old.)
You don't want your 13-year-old wandering round dark streets risking life and limb as the pubs close. But you can't really object if your 18-year-old wants to do it. He or she is legally an adult, after all.
So there aren't many things that are true of all teenagers.
Except for staying in bed till lunchtime. I think they're all pretty good at doing that.