> insanely toxic
Some quick searching suggests that it’s toxic but not even close to “insanely toxic”. And it’s not persistent in the environment.
If you want a genuinely nasty chemical, check out methyl isocyanate, which is some two orders of magnitude more acutely toxic.
I'll see your CH3NCO, and raise (CH3)2Hg -
https://en.wikipedia.org/wiki/Dimethylmercury#Safety
- considerably more deadlier, and the mercury an element - so no clever chemical reactions can break it down into innocuous CO2, H2O, and N2.