Dying while easting a Double Down from KFC. You're in heaven from eating it and you won't notice anything else.
The U.S. Centers for Disease Control (CDC) gives a possible minimum figure of 500 micrograms (about half a grain of sand) for the lethal dose of ricin in humans if exposure is from injection or inhalation.[1]
i think the most painless way of dying is quick beheading.
If it's quick.. you'll lose instant access to the pain processing center in your brain.. so you wont know if yer in pain.