It is another term for a dirty sexual act, the Choco-taco has gotten it's name when a male decides to take a "dump" into the female partners vaginal insides.
Daddy: Come on sweety, you want your choco-taco?
Daugher: Daddy, what's a choco-taco?
Daddy: Well hunny, spread your legs.
Daughter: *spreads legs*
Daddy: *Takes a poop in her vagina*
Daughter: Daddy, why did you just poop in my hoo-hoo?
Daddy: Well sweety, I was showing you what a Choco-taco is.