When you insert your thumb into another person's orifice, mainly the anus, resulting in pleasure. Usually only done during sexual activities, the phrase was made popular when Kentucky Ballistics 50-cal blew up, and he had to put a thumb in his next so he wouldn't die.
The badass Kentucky Ballistics almost died to a 50 BMG SLAP round, however, his thumb plugged the hole of where his jugular was sliced.
This fateful accident led to the term the "Kentucky Plug" which appeared on a meme in Brandon Herrera's (The AK Guy) YouTube Series Gun Meme Review.
The Kentucky Plug is when you ram your thumb so well into a woman's vagina that there is no possible way for her to excrete any fluid from it... This maneuver is only accomplishable by few men, and makes the woman uncontrollably moan in pleasure, often times saying "SCOTT, YOURE THE 500 MAGNUM MASTER" much to Demo Ranch's protest.
The Kentucky Ballistics lifesaving technique that doubles as a sexual innuendo.
Performed by locating the hole of choice on the subject body, and jamming a thumb in said hole with all available might. The thumb cannot be removed for several hours.