"To front on" is a slang expression; it means to lie, to act with false bravado. It can also mean to challenge or confront someone, to stand up to them.
"Don't be frontin', you know that pimped-out Cadillac ain't your ride."
(Don't pretend that that fancy Cadillac is your car.)
"I'm about to smack you up for tryin to front on me in front of my peeps."
(I'm going to hit you for attempting to challenge my authority in front of my friends.)
- For Teachers