Okay, then. If you're absolutely sure.
Just use lighter fluid to douse yourself. You can get it at any hardware store. About 1–2 gallons or more should do the trick, in my opinion.
I would recommend soaking thick pieces of clothing (e.g., a coat, sweatshirt, jeans, etc.) in the lighter fluid first, then putting those clothes on for ultimate coverage. This will give the fire something to burn through for a while. And make sure you have multiple layers of these soaked clothes. After you have your clothes on, shower yourself with the lighter fluid.
Also, when you do set yourself on fire, make sure you're far away from everyone else. People will most likely try to put out the flames as quickly as possible, leaving you with severe burns.
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I forgot to mention not to wear too many layers of clothing. Lighter fluid needs oxygen to burn. So 2–3 layers should be enough.