A sexual act that involves a male inserting his thumb deeply into the genetalia of a female. This maneuver can be done while the female is on her period to maintain authenticity to the incident it was named after.
"My husband and I were getting frisky yesterday. He was sad when I told him that I was on my period but soon got excited once more when I offered for him to give me the good Ol Kentucky Plug."
Used in the throes of passion during intercourse, usually in the doggy style position. Generally understood as penetrating the bent over partners anus with the thumb.
She told me she wanted it in the ass, so I gave her the ol' Kentucky Plug.