When you ask someone to turn on or turn off the AIR CON.
To me, it makes perfect sense to shorten "air conditioner" to "air con." But, in the mainland, people look at me as if I were from Mars when I say it. For them, it's the AC. I found one person born and raised in California who didn't think "air con" was a weird word, and he was Filipino by blood.
Sometimes I call it the "air con dåkdåk," something I learned from somebody else. Dåkdåk is an actual word and it means "to knock," so linguistically it doesn't fit. Still, it sounds funny. And Lord knows we all need a reason to smile day to day.