A word that hillbillies/rednecks use because they cannot pronounce the words "fuck" and "you" properly, so it comes out "fuck ya'll." I believe it stands for fuck you all if you take out the contraction, but then that just makes it sound even more retarded, so I will just say it's "Fuck ya'll." It's commonly used in the phrase, "Fuck all a ya'll!" which translated into proper english means "fuck all of you all." I'm not even going to go there, so have a nice day =]
Redneck: Hey ya'll
Group of people: Go away you fucking redneck!
Redneck: FUCK YA'LL