Ballpapering
This is when your smartphone is hijacked (usually by a friend because you were stupid and didn't secure it with a passcode) and a picture of (usually their) genitals is used as the wallpaper, particularly the lock screen.
We are ballpapering johnny's phone with a picture of a big black penis found on google.
Ballpaps
When a sexual partner smacks your balls and it makes that pap pap pap sound.
I love it when my lady gives me ballpaps whiles she's suckin