In America, tipping is an integral part of the restaurant experience.

As someone who used to work in the service industry, I’m known for being an over-tipper. However, for people from other countries, those who didn’t grow up eating out, or teens trying to navigate the rules, tipping can be a confusing practice. How much should you leave, and what’s it based on?

The standard tipping guideline is 15-20 percent of the pre-tax bill. Recently, one waiter was surprised when he received a tip far below that amount after a pleasant interaction with four teenagers. What he didn’t expect, however, was what happened a week and a half later.

The waiter, who has been serving for a long time, shared his experience online, expressing frustration at being thanked profusely but then only receiving a $3.28 tip on a large bill. The teens had clearly enjoyed their meal, but the tip seemed off for the service provided.

A week and a half later, one of the teens returned to the restaurant, bringing a note and an apology. The note explained their mistake and included $18 and some change as an additional tip. The waiter posted this online to express his gratitude, thanking the teens for taking the time to educate themselves and making the effort to correct their initial oversight.

Dear Mr. Waiter,

About a week and a half ago, on October 7, my 3 friends and I came to eat at this restaurant as our own homecoming celebration. It was an exciting experience for us to be here alone, and it was all new to us. And you were the best waiter we could ask for. You were kind, helpful, accommodating, didn’t treat us like babies, and were even able to fit all the food to all my allergies!

So I wanted to say thank you for making our “grown up” experience so amazing and fun. I would also like to say sorry on behalf of my group. Since we were new to this, our 13 year old minds didn’t exactly know how to deal with the bill. You were super helpful in dividing the check up and taking our not-so-preferable cash. The bill was reasonable, but we had completely forgotten (and frankly didn’t know) what a tip even was, let alone how much to give.