When you stick your thumb down your sex partners throat at the point of climax
Oh bro I was with this girl last night and when I was about to nut I blew my 50 and stuck my thumb down her throat that's right I have her the kuntucky plug
An act involving a thumb plugging a hole. Pressure significant enough to stop blood flow is required. Sometimes used to save lives. Also used for pleasure.
I gave her the Kentucky Plug to save her life. His prostate was tickled with a Kentucky Plug for fun.