Even for Farrah Abraham, the revered Cannes Film Festival is just another day at the office -- as in, a place to flash her fully exposed crotch to the masses.

The ex-'Teen Mom' and porn star not only went commando Monday night while attending a fashion show -- she made sure to shift her gown so everyone would know she was au naturel ... as they say in the South of France.

Y'know what else they say in France? Sacre bleu! Zut alors!! And put on some damn underwear, lady! Look, it's not unheard of in celebdom to go nude under a couture gown, but most manage to keep their vagina out of the picture.