I would just tell them next time. I treat my teens' friends slightly more politely than I do my own kids, which means that instead of an acerbic "did you stop to think how I was going to wash out those stains?", they'll get a pleasant "guys, please don't put your napkins inside your plate, it's hard to wash out the sauce". I would explain the reason, to help them remember. This is how you raise well-informed adults.

Anonymous wrote:I suppose I have to ask, why are you rinsing them?

DP. You want to remove any extra tomato sauce before tossing in the washer so it doesn’t stain anything or everything else in the load. I also pretreat each stain because otherwise it might not come out.

https://www.cleaninginstitute.org/cleaning-tips/clothes/stain-guide/tomato-sauce-and-spaghetti-dinner-stains

I suppose I have to ask, why are you rinsing them?

Agree with PPs that the teens are probably trying to be polite.

Also agree with PPs that napkins on plates are impolite (I think so gross) - both cloth and paper. Hate it. Also hate when folks “ball up” a dirty napkin and leave it on the table. So gross for everyone else to look at. Use it nicely, don’t be a slob, dab at your mouth, leave it on your lap until the meal is over and you clear your plate (or leave it neatly folded by the side of your plate).

If you’re using that much of a napkin it’s a signal you are a sloppy eater and need to work on table manners. Unless you are shucking crabs or at a crawfish boil or something.

Anonymous wrote:My kids get black cloth napkins for this reason. The kind restaurants use.

Lol, same

Just casually ask them to leave the napkins on the table when they’re finished and not on the plate. They probably are clueless about laundry stains.

Teach your kids the correct etiquette which is to place cloth napkins on the table to the left of the plate when you are all finished eating. If you get up and leave the table but aren’t finished with the meal yet, the napkin should be left on your chair.