To involuntarily put a spot on your underwear with your feces.
<Walmart customer in check out line> Can you speed it up, I'm about to bingo stamp my underwear?!
To stamp someone in the face with your erect, moist, bell end.
The aim of bingo stamping is to stamp someone five times anywhere on the face with the final stamp being inserted in the mouth, where the bingo stamper shouts BINGO!
James: "Played bingo stamping last night with the missus"
Nathan: "How did it go?"
James: "The girlfriend loves playing bingo stamping, got her twice on each cheek, once on the forehead and then got full bingo in her mouth. It was great!"