A tuck is a procedure that is performed when one's scrotum is far too large for the testicles they contain. The excess bag is folded or "tucked" upwards and then sutured or stapled in place. In addition to being the name of a medical procedure the word can also be used an an insult. This insult can be used when you detect the sand in someones clam or they are such a douche you can assume that its because they are tripping on their sack.
-You have a huge scrotum, you need to get a tuck.
-Man that guy needs to get a tuck.
-Tuck your muff you douche bag.