phrase, the meaning of which changes quite significantly depending on context
If said to you by someone else, it can mean "knock yourself out" or "wow, that kicks ass!", as illustrated below.
"Can I consume what's left in those liqueur bottles in your liquor cabinet?"
"Go the hack."
"I just consumed two bottles of cheap liqueurs!"
"Woah, go the hack!"
If said by you, it generally indicates that you intend to take something to its natural conclusion, or go the whole nine yards. It can also indicate an intention to put in significant effort.
"I'm gonna go the hack on all those half-empty liqueur bottles".
"I suppose I could come out and get smashed tonight, but I'm really going to have to go the hack on that essay tomorrow."