At the carwash, I wanted to ask the teenager a few choice questions.

Why were you on your cell phone while washing your car? Why did you put down the phone, turn off the sprayer, search your pockets for quarters, then leisurely walk to the change machine? Why did you stop the sprayer again, open the trunk, and pull out some rags? And after finishing, why did you carry on another cell phone conversation for a good minute or two while still parked in the washing bay?

Perhaps I was in a particularly bad mood that day, but the longer I waited in line directly behind the teen, the more irritated I became. When he was done talking on the phone and driving away, I thought of one last question: Why hadn’t you learned some car wash etiquette?

In this particular case, there was no question in my mind that the teen showed a lack of consideration and respect for those waiting in line behind him, whose time was as valuable as his. But there was also a money aspect to this situation.

Let me explain.

I understand why many parents might not feel qualified or confident enough to immerse their kids in the finer points of money management, investing and consumerism.

However, I think many moms and dads are more than qualified to talk to their children about the etiquette aspect of money, such as showing up at the car wash prepared to get the job done.

Since my experience at the car wash, I’ve spent a bit of time analyzing financial manners and how to help children act appropriately in these sometimes delicate situations. Here are five examples that parents and kids face all the time and some approaches to consider.

Check the check. When you dine out with the kids, explain that it is important to check the bill and leave a tip that reflects what you think of the service. Fifteen to 20% is a standard tip at restaurants, and letting the kids do the math at the restaurant is a great way for them to see the process in action.

Also, make sure the children understand how waiters and waitresses are paid, typically a low hourly wage plus tips. With prom season under way, many teens will be dining in groups and splitting the bill and they’ll need to remember to carry enough money to contribute to the tip tab. On numerous occasions, I’ve seen teens stiff the wait help, then snicker about it on the way out the door.

As for kids text-messaging on their cell phones at the restaurant, well, that’s another column.

Popcorn and Milk Duds. When our kids are invited to a movie or ballgame, I try to remind them to take enough money for their ticket and treats, unless it’s an obvious invite where a parent will be footing the bill. If parents do pay for the ticket, tell your kids to offer to buy the treats, so they can contribute something to the night out, said the author of “Cash Management for Kids,” Maureen Dolan Rosen.

Duplicate gifts. “Oh, I have it already.” How many times have you heard those words blurted out by a child at a birthday party or holiday gathering? It’s nothing intentional, but it can take the wind out of the gift-giver’s sails.

Ms. Rosen offered a better approach for a youngster: “Thank the friend or family member profusely and act as if you’ve never seen the gift before.”

Thank-you notes. Are notes for birthday and holiday gifts required in your household? They should be. I’ve talked to numerous people who say nothing is more disappointing than sending a gift to a child to which there is no response.

I used to be a stickler for handwritten thank-you notes, but e-mail will do. It’s the words that count.

Gas money. A lot of college students will be bumming rides home in the next few weeks from friends, and they need to remember to fork over money to cover gas. The driver shouldn’t have to ask. With gasoline prices edging ever higher, not offering to fill the tank can create hard feelings, and the carpool offer might not be extended next time.

If you still think this is common sense stuff that kids will pick up on their own, I hope your son or daughter isn’t in front of me at the car wash next time. I just might get my blood pressure up enough to offer an etiquette lesson or two.