Literally: Go fuck an ass in Italian slang.

Used as "Go fuck yourself!"

lil mad is like big mad but the opposite, you mad but not mad to the extent of pullin somthin

Literally: Go do a ass

Va' means "you go" and comes from the Italian word "Andare" which means "to go"

Fa' means "you do" comes from the Italian word "Fare" which means "to do, or to make"

un, is the indefinite article "a" in masculine form.

culo, means behind, or can be slang for bottom, or "ass"

"Va' fa'n-culo" in the roman pronunciation.