Damn that's cold. I didn't even know Kelvin had a negative scale, that would make it roughly -490F wouldn't it?
Or are we into a whole new scale at that point.
I think he was joking, but negative temperatures on Kelvin scale actually do exist. However such temperatures can not be achieved by traditional means (ie. "cooling). I'm not good at explaining this stuff, so here's a related article I googled http://www.maxwellian.demon.co.uk/art/esa/negkelvin/negkelvin.html
considering that absolute zero in farhenheit is -459 degrees I am guessing it is something like -530 degrees farhenheit, without a calculator handy could be more could be less.