1) A personal email message, as opposed to a business or commercial email message.
2) A love letter, billet doux, or personal missive sent electronically.
In English, this word was adopted from French due to the lack of distinction between personal and business email usage; the French word simply means "email". In 2003, the Académie Française (French Academy) chose "le courriel" - pronounced "koo ryehl" - as the official French word for "email," but that does not necessarily mean the French person on the street uses it regularly. As noted in the second definition, in English the word can imply a romantic or deeply personal message.
I received a few unexpected courriels today from friends, all of which brightened my day.
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.