I would disagree with this one. I know most people say "same difference" when comparing TWO things, but when used properly, that phrase is NOT an oxymoron: Say you have 4 items we will call A, B, C, and D. If you compare A to B, and get the difference, there's ONE difference. Set it aside. Then, if you compare C to D, and get that difference, there's ANOTHER difference. Compare ONE to ANOTHER, and if they are the same, then you have the "same difference." If ONE is not the same as ANOTHER, then we do not have the SAME DIFFERENCE, but it is a negated phrase. "Same Difference" is not an oxymoron.
oxymoron - A rhetorical figure in which incongruous or contradictory terms are combined, as in a deafening silence and a mournful optimist Just for reference since some don't seem to get it..