circa 1970s American slang

1) to party
2) to have sex
3) to dance
4) to abandon nonsense and confront

The phenomenon of having to come out as bisexual to the same person/people repeatedly because they assumed or hoped that your sexuality was a "phase." Refers less to the holiday and more to the 1993 Bill Murray comedy film in which the main character experiences the same day over and over.

During the disco and funk era, in many venues the dance floor was often located below the seating area, so to "get down" was to go down to the dance floor. Originally meant in reference to dancing, eventually leading to sexual implications. However, it also means "to be cool with".
A most useful term.

Other forms: Get down, gettin down, getting down.
There is a more recent version of the sexual meaning is "going down (town)".

An action, depends on race. See example

A certain act that must occur on Friday. The first human being to enlighten us as to the obligatory nature of this act is Rebecca Black, a distinguished artist who lived in the 21st century.

an expresssion that arnold schwarzenegger likes to use a lot

To begin foreplay, sex...
Usually in association with cutting all the stupid games and getting straight onto some physical action.