Green’s Dictionary of Slang

(US campus) to vomit.

1975		G. Underwood ‘Razorback Sl.’ in AS L:1/2 60: He makes me want to hack.
2009		N. Flexner Disassembled Man [ebook] I woke myself up by hacking a pint of blood.
2009		T. Black Gutted 82: The boys were silent enough, save for the times when they started hacking their guts up.