Ninjas use all sorts of crap to kill themselves... (guns, ropes, knives, lasers, spears, etc.) and don't even think twice about it. These guys would kill themselves for just about any reason and often for no reason at all: that's why there are so few ninjas today.
But if you want to commit Seppuku and you're like me, you don't have access to stuff like lasers. But there's hope. I tried to kill myself by swallowing a frisbee a couple of times, and believe me, it's pretty cool. The only catch is you have to be really super pissed to do it.
Step 1: Get a frisbee from the store or friend.
Step 2: Clean the Frisbee.
Step 3: Make sure your parents aren't around
Step 4: Put something slippery on it, like butter or cream.
Step 5: Get really super pissed.
Step 6: Fold the Frisbee hard (this is crucial)
Step 7: Keep folded and insert Frisbee into mouth hard.
Step 8: Push hard until you can't see it.
Step 9: Wait.
Step 10: Die.