If I were invincible I wouldn't die, I'm invincible, you wouldn't die of old age.
I'd play chicken with trains and scare the sh*t out of the driver. Have him hit me then pop up on the window on front of him.
Find Ben Stiller, Kidnap him, take him to a desert Island and bring only a video camera and enough food for one person. The only way he can eat is if he makes me laugh. He'll die of starvation.
fall in the bear pit at the zoo. Then when they get me out I "accidently" fall back, again, and again, and again.