Full page pictures in "Prude" Magazine featuring someone (male, female, or somewhere in between) being anally penetrated in an atypical manner.
The term became an interjection used most often by intoxicated party-goers in rural areas in Western New York during the late 80's to express their chemical induced euphoria. The expression's usage faded with the demise of the magazine.
An 8" x 10.5" glossy picture of a Cossack she-male being anally violated with a corn cob by a midget dominatrix. No text appeared on the page other than "ANAL BONUS". Anal Bonus pages were not included in the Table of Contents.
After multiple funnels of Genny Light and hooking up with a biker chick, Brian staggered back from getting blown on the shores of Lake Ontario and exclaimed "Anal Bonus!" when his pals came into view.