Obscenely tight fitting gentlemen's under crackers, generally worn by Olympic dive teams and East European 'female' gender-check shot putters of the 1980's. So named due to the slapping effect on the base of the wearers testicles during the pike phase of both events.
Now more commonly found on the beaches of Southern Europe on an overweight greased up German, also see banana hammock or Speedo's for the beach variant.
"Klaus ist miner packet g-boolljen?"
"Yah das ball smackers hast kleiner Willhelm in der knutter cracken" (insert overtly exuberant laughter)