Is usually when yall get together with a bunch of friends and have a howlin' good time. Music, lots of booze and wild abandon are key ingredients. May be organized by some social group or establishment in the hopes of attracting many strangers/patrons.
Term has its roots in the traditional dance performed by some folks long ago.
Jimmy: Yo you goin to the Pit? they havin' that blues night hodown!
Jack: Nah man...they don't know how to throwdown.
Jill: Yea and they really overcharge u on watered down drinks...hey lets just get a shitload of food n booze and get the whole crew to hodown at JJ's.
When your wife pisses you off to the point you throw her on the ground.
Jimmy Raisinberry: ZENA! YOUR CAT IS KILLING ME!
Zena: MY PUSSY!!!
*Johnny throws her down perfusely* BITCH! HERES A HODOWN!