fat a tat tat Share definition Flag A phrase that is often said when an MSN conversation between Ashley Aubertin and Allison Del Vecchio has a font size of 16. Allison: Size 16 yo! Ashley: Fat a tat tat. fat a tat tat by Ashley_A October 23, 2004 0 0 Get merch Get the fat a tat tat mug. Buy Now — $32.95 See more merch