Much like that of Thirsty Thursday, it is a day to enjoy spirits and other intoxicating substances to prepare for the coming Friday generally with a group of friends you would spend Friday with. It may also include a sort of fight in the backyard or during the party hence the other meaning of "Throwdown." Lastly, everyone must throwdown some money for the booze, it's a BYOB without the hassle.
Comes from the phrase "To throw down the gauntlet", which means to issue a challenge. In medieval times a knight would throw his armored glove, or gauntlet, at the feet of another knight to challenge him to combat. If the knight took up the gauntlet he accepted the challenge.
When you bang a girl on top of a high dive or platform above water while she is in backbend position, when you finish you grab the poor girl's legs and flip her into the water.
Troy: "Dude last night i snuck into the local pool, and gave my girl a pacific throwdown!"
Andrew: "Damn dude thats awesome!"
A Barber Shop Throwover is the act of masturbating while under the concealment of a barber or salon apron during a haircut or other cosmetic treatment. A proper Barber Shop Throwover is performed with enough stealth and subterfuge as to not attract the attention of the hair professional. Nomenclature may differ widely based on geographical region, but Barber Shop Throwover and its associated etymology is considered the proper descriptive term.
Having received a raging boner from the hot female stylist, the man executed a Barber Shop Throwover with ninja-like precision.