When a large-limbed man wears swetpants or shors without underwear, his penis being wacked/slapped from left to right by his legs when walking, or by both hands in his pockets
I had a half-boner earlyer. I tought i might sign up for the pockettennis league
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.