Generally, an instance where luck works against you in a game at the worst times or with no apparent justification. This can include tabletop rpgs or video games. A combination of the words bullshit and critical hit, usually shorted to crit.
Originally from Team Fortress 2, which uses a random critical hit system, and referring to the Soldier's devastating crit rockets in particular.
One second I'm an overhealed Demoman, and the next a Soldier with 5 hp one-shots me as he rounds the corner. It's pure bullcrit.
When I saw Matthew coming out of Troopers, the gay bar, draging an effete young thing on Friday, and then saw him hustling Melisa on Saturday night, pinning her in between the pinball machines, I knew the rumours of Matthew being a bull fruit, willing to screwanything, where true