The Bog is the area between the genitalia (usually male) and the asshole. This area is also known as the Taint
but when it is particularly sweaty, slimy or not clean it is referred to as "the bog".
After having sloppy sex all night and then going for a jog. Kenny declared, "Man, my bog is sweaty."
Alan had a sweaty bog because he refused to shower for a week.