An invitation to celebrate and let go of one's cares in an idiosyncratic and inexpressible idiom. Alternative to the more straightforward/common "party hearty", and its variant "party hardy". Neither negative nor positive in connotation, neither zealous nor blasé. Like the Tao, cannot be explained further without destroying its meaning. Most often used as a greeting or toast, it can serve almost any non-expletive purpose.
Example 1: Dave (toasting the first guests at a gathering): Party shit.
Guests: Party shit.
Example 2: Jeff: It looks like they left an 'r' off your "party shirt".
Steve: No. They didn't.
Example 3: Mark: Why does it say "Party shit" on these cocktail napkins?