This is just an expression one can use to express pleasure when something has happened or will happen that is so amazing or cool, but you desire to use a term a little stronger than nice, sweet, awesome, etc; you use the term "Sugar on Tits".
"Dude, if this amazing thing happens to me next week, it will be so fricken awesome. Could you imagine?" says one guy
"I know", says the other, "It'll be so fricken sweet, it's like Sugar on Tits." THAT'S SWEET!