It was resurrected by the "USC Mafia" in school elections before they joined the Nixon administration and perfected the practice; it means to utilize dirty tactics (i.e. stealing ballots, changing the time of events with organizers, etc.) in political campaigns to win at any cost. This practice eventually led to the Watergate scandal and Nixon's resignation.
Carl Rove is a true rat-fucker.
Term is used in the Infantry division of the Army when someone opens up an MRE (meal ready to eat) package and only takes the candy/cookies. This leaves the next person to a meal with no treat.
"Who ratfucked the Costco potato chip assortment and only took the Doritos?"
"You dick. You ratfucked the mini-cereals and only took the Apple Jacks".
1. Slang. To rifle through something taking the one special part out of it leaving the dregs behind.
1940's era US Military, most likely the Army.
rat fucker, noun
2. Damn! My dad rat fucked all the cashews out of the mixed nuts again!