pig switch 

noun: a person who by all accounts is perceived to be genuinely good, but by one decision becomes a scumbag.

verb: an act of turning into a scumbag in a split second decision

Tiger Woods was considered a genuinely awesome guy by society, until he pig switched by railing a bunch of skanks and blamed it on his "sexual addiction."

pig switch by ayshwondinglefuss October 13, 2014

pig switch 

A switch fitted to the inside back of our heads (possibly placed there by aliens) which will be operated when a certain amount of alcoholic beverages have been consumed. Once the "pig switch" has been operated, a man's behaviour will become very erratic, generally he will cease drinking with his buddies and go on a mission to get laid with any female that says "yes". As a rule of thumb, these females will be ugly in the extreme.
WARNING: Women can often sense when these switches have been activated (possibly by being in tune with their ovaries), and will often use this time to facilitate an impromptu marrage proposal.

Ben: What happened to you last night Bluey? You were there drinking with us and then all of a sudden you dissapeared.
Bluey: I'd had so much beer that my pig switch was activated. I wandered in next door to the disco and picked up the first chick that would go with me. When I woke up next to her this morning I discovered that she was an absolute 3 Tusker

pig switch by ulb remorse October 21, 2009

pisswitch 

Acerbic female, usually bitter and twisted . Quite often anti-social. Stays in and posts on internet forums all day.

'When she talked, she came across as a right little pisswitch'

pisswitch by ans August 26, 2004