Green’s Dictionary of Slang

hachi n.

also hatchi, hotchee, hotchy
[Jap. shakuhachi, 50cm (20in); imported by US veterans of the Korean War (1950–53); but note hatchi n.]

(orig. US milit.) the penis; thus eat/suck a hachi! go to hell!

A.M.Z. Norman ‘Bamboo English’ in AS XXX:1 47: From the Far East to Germany, wherever the U.S. army has soldiers, in fact, the phrase suck a hachi is heard.
(con. 1950) John Algeo ‘Korean Bamboo English’ AS XXXV:2 121: Suckahachi or I’ve got your hachi, ‘go to hell’.
[US]B. Rodgers Queens’ Vernacular 102: hachi [hatchi, hotchy] (GI English, fr Jap hachi = eight + pun made upon sl ate & hot: used by GI’s with native women: ‘Me likee numbah one hachi’) homosexual soldiers, choosing a penis over a vagina, used the word to mean cock.
Cagg Lex. Militaris 222: Hotchee. The penis. Widely used in Korea [HDAS].