During mutual oral sex or "69ing" with the male on top, testicles drape over the nose of the partner on the bottom, covering the nostrils and impeding airflow.
Damn, when I was 69ing that bitch, I gave her such a nutt smothering that almost passed out.
Your significant other is snoring too hard or passes out early. You ride the face until he/she starts passing out. Once the convulsions start, then You step on their junk to revive them.
Todd snored so hard he deserved a smothering majora from his wife as retaliation for the gladiator helmet she received once.