When you launch semen in a girl's booty and throw her on the sand. The sand or dirt* then sticks to the released semen and creates a sandy ring or "sandy bagel" around the butthole.
*Advanced Technique: Evolves into a Dirty or Muddy Bagel
Man 1: Hey you remember that Hella fine girl from that beach party?"
Man 2: Hell yeah bruh she had dat booty fo sho"
Man 1: Long story short...Gave that bitch a Sandy Bagel!"