Where you drop your trousers part your butt cheeks and kiss somebody on the cheek with your puckered anus
You remove your pants, spread your butt cheeks and move closer towards the person, close enough so that your anus is almost touching their cheekbone. Either side is fine. Then, provided you've shat recently, push out your anus a little so that it forms a pucker and the propelled anus bit touches the recipients cheek.
This is a Dragon Wink.