Large anal expulsion of gastrointestinal gasses post coitus on any sand covered coastline.

After a long day at the beach you fart in someone's face, thus blasting sand all over their face.

When you jizz on a girls face and throw sand on her. LOL

A girl with a mouth full of sand gives a guy a blow job, and his shaft is scrapped uncomfortably by each individual grain. Needless to say, the experience isn't enjoyable for either party, and the couple is hopefully wasted on a beach - otherwise why the fuck would her mouth be all sandy.