X <- data.frame(Variable1=c(11,14,12,15),Variable2=c(2,3,1,4))
> X
Variable1 Variable2
1 11 2
2 14 3
3 12 1
4 15 4
> X[X$Variable1!=11 & X$Variable1!=12, ]
Variable1 Variable2
2 14 3
4 15 4
> X[ ! X$Variable1 %in% c(11,12), ]
Variable1 Variable2
2 14 3
4 15 4
You can functionalize this however you like.