What is it called when you ride a bmx like a unicycle? I was looking around a bit on YouTube and found a video for a footjam decade... which is pretty cool, in my opinion. However, in this video at 2:44 he rides the bike like a unicycle, straddling the head tube with feet on the pedals... which is freaking cool. What would that even be called?
According to this site on artisitic cycling they refer to a trick called a "head-tube wheelie" which is probably a good name for it. BMX enthusiasts may have a different name for it, but that's essentially what it is.   I was also able to find this other site referring to headtube wheelies.  Also, this Youtube video refers to it as a headtube seated wheelie, and headtube backwheel riding.

After some Googling with the help of @dotjoe's answer, I've found that this trick is referred to a "Pedalling Death Truck" or a "Blender".  There's also a trick called the "forwards spinning deathtruck" which is pretty much the same thing except the rider faces the other way around (at least as I understand it).