When two people are engaged in sexual intercourse and one person rams one of their thumbs as hard as they can into the other person's anus, shouting "YEE HAW".
Yeah I gave her the ol' Kentucky Plug last night, she wasn't too happy since my thumbs are even bigger than Megan Fox's.
A Kentuckyplug is typically used and was invented in the great state of Kentucky. This is a sex move that involves the man using his thumb to pleasure his girl/significant other.
Oh man, I have her the good old Kentucky plug last night and she loved it.