The next time you do your laundry at the Laundromat, leave a couple of quarters behind for the next person. You could even leave them on top of the machine with a note saying "Have a great day!"
You will leave the laundromat smiling; you will never regret not having those couple of quarters later. And it's pretty likely that the recipient of your kindness will leave smiling, too.
Make it a practice to do this every time you go to the laundromat. Perhaps the next time you go, offer to take your friend's, roommate's, or neighbor's laundry, too. Pay for it and return it clean and folded.
Why stop with the laundromat? Anytime you go to the self car wash place, an arcade or use a vending machine...wherever you go that you are required to use quarters, leave a couple of extra with a note behind.
If you have a washing machine and dryer, let a friend, neighbor, or roommate wash their clothes at your house or apartment for free. Spend time with them while they are with you! Watch a movie or eat dinner.
Read up on Laundromat etiquette.