jankum is when you take a somewhat large crap and put it in a bottle with a balloon on top and after a few days of extreme heat sniff in the gas' that have accumulated in the balloon go into a state of being high
piss, shit, vomit, and other bodily fluids are put into a pastic bottle with a ballon on top. the bottle is left in the sun resulting in foul gases collecting in the ballon. this foul gas filled ballon can then saposedly be inhaled. only a retard would create or do such a thing.
If you are playing Battelfield 3 and you get splattered by a MAV then you would stick your middle fingerin the air and shout "That's BO-jankus!", or if you were about to get a double 360 YY Backspin, ladder-stall, no scope/pro-scope, and you are killed by c4.