Well i'm not entirely sure to be honest. It's presumably derived from technics 1210, the Ford Sierra of decks used by every DJ from fatboy slim to the fatboy slim wannabe running your local church under twelves' disco.
The phrase has been popularised by irish Sp'o'iral in the UK big brother #7 in reference to wannabe ghetto princess Aisleyene (sic.) and some part of her body. She does have big fakes boobs and shows her ass quite a lot, so i guess it's one or other of them. Look at the example and see what you think.
Ais's got the twelve tens going on and i want a sl'o'ice.
Sl'o'ice being a irish internation of slice, as in her ass is like her loaf of bread and i want a sl'o'ice. (his phrase, not mine.)