When a friend of the opposite sex (for heterosexuals) wears something slightly revealing or otherwise shows a bit of skin, and it would be rude or confidence destroying not to take a quick glance.
Claire just got changed on the bus, would have been rude not to give her a courtesy perv
When you are watching a movie with a bro and a sad part comes up. Your bro begins to cry so you throw your drink in their face so no one can see that he is crying.
Dude, thanks for that courtesy splash when Obi-Wan died. I would have been hella embarrassed.
A job for High school kids which consists of; cleaning the store, cleaning the bathrooms, collecting carts, sweeping the store,and giving customer assistance-for very little pay.
The courtesy clerk fell down on frozen aisle, while doing his sweep.