1.)A crab shit is when you have to take a mean shit and you have to mount the toilet and put you whole body on top of the toilet seat in a back-wards crab position.
billy: hey alex
billy: why is there footprints on my toilet seat?
alex: oh i was just taking a crab-shit why?
billy: ok well theres poop on the seat to...
alex: ya i sliped