A large crease that is native to the gut of an obese person, beginning at the navel and continuing towards the nether- region, resembling a vagina. The fatty tuna is not relegated to either sex, but instead, fat people. A synonym of "Frutt," or "front-butt."
"Once she lifted up her shirt and I saw that fatty tuna, my boner turned inside-out."
by tim_the_terrible August 07, 2007