Mariah Carey -- In Your Face, Packer ... with My Backup Dancer!!! (VIDEO)

Mariah Carey showed James Packer who's boss Thursday night by chowing down with the guy who made her ex-fiance crazy. Mariah sushied out at Nobu in Malibu with Bryan Tanaka, the backup dancer who got super flirty with her ... so much so Packer had…