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!
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".