First of all, this is a harm reduction forum -- it would be a violation of its terms to tell you how best to hurt yourself.

There are easier and "healthier" ways to just get fucked up if that's what you're looking to do, but I humbly recommend that you consider the reason behind your desire to simply obliterate your consciousness.
Secondly, MDMA doesn't have a linear dose/response curve; there's a point at which taking any more won't increase the main effects. The speedy effects are slightly more linear, but those too will taper off.
Finally, the LD50 (the dose at which half the tested population die) for humans hasn't been established, but it's speculated to be anywhere from 10mg to 80mg per kilogram body weight. Assuming it's 10mg/kg (and I guess also assuming no tolerance), the LD50 for a person weighing 150 lbs (68kg) would be approximately 680mg. People with ridiculous tolerance take many times this amount of MDMA on occasion, so I imagine the LD50 is a little higher.
Again, I have to say that you're not going to get much out of getting near an OD on MDMA -- in fact, it may make the roll shorter-lived and much, much less enjoyable if not outright horrible. Please consider this, even if you don't care much for your health.
