Hiri-Kara? Heni-Haha? Caca-poopoo? Dictionary.com has "hara-kiri" and "hari-kari". It's part of their new line of "ingrish" transliterations.
BTW, you don't need a knife. A frisbee works just fine:
http://www.realultimatepower.net/index3.htm
(then click on "Seppuku"😉