Best post in weeks! Here are a couple of links that explain it all. With some definitions that don't quite fit.
"This article refers to the kayaking term. Boofing may also be a slang word for sexual intercourse, particurally anal sex.
In whitewater kayaking, boofing refers to the raising of a kayaker's knees, while applying the final paddle stroke, when approaching a waterfall at speed. This technique is used to avoid submerging the kayak by ensuring it lands flat when it hits the base of the waterfall. The term is believed to be an onomatopoeia derived from the sound that is sometimes created when executing the maneuver.
Boof can mean a variety of things, from a hard hit, to the word you yell when an opponentÂ’s team is taking foul-shots. This word has been further banned from being used because it's thought to be an "inappropriate" word.
The term boof or boofhead can also be used in a derogatory manner directed towards people that one finds annoying.
To boof is also to partake of Crystal Meth.
Boof is also a slang term for affectionately hitting someone over the head, such hitting is often derived from the Blackadder II show, where Lord Flashheart would kick his associates and shout "Woof!".
To boof is also to flatulate. The term is an onomatopoeia derived from the sound that is often created when one passes gas."
OMFG! Anal Sex! I'm quitting kayaking if thats involved.