To bitch shift : sexual activity involving a group of men each in turn having sex with a larger woman. Upon ejaculation, the man is said to "Shift The Bitch" to the next man, who will repeat the process until every man involved in the event has ejaculated inside the woman.
Added man points if when 'shifting the bitch', the men also roll her over. The fatter the chick, the more fun the bitchshifting is for all parties concerned.
Then it is said the woman has been 'bitchshifted', the men were involved in a 'bitchshifting', or perhaps that they spent their evening 'bitchshifting'.
8 friends bring one woman back to a motel, then one by one the men have sex with the woman and have themselves an 8 man Bitchshifting.