Justin Bieber's Neighbor -- HE SPIT IN MY FACE!

Justin Bieber spit in his neighbor's face and threatened to kill him, after the neighbor dared tell the singer he was driving recklessly ... that's exactly what the neighbor told Sheriff's deputies.

Law enforcement and neighbors tell TMZ ... Bieber hocked a loogie in the man's face during a heated confrontation Tuesday morning. We're told Justin's Ferrari had arrived on a flatbed truck at around 8:00 AM and Justin decided to take it for a ride in the gated community. A number of neighbors say Justin was driving insanely fast -- the complaining neighbor says 100 mph.

The man -- a 47-year-old successful businessman and father of 3 -- went onto Justin's Calabasas property and screamed, "You can't drive like this!" The man told deputies, Justin responded by saying , "Get the f**k out of here," and then he spit in the guy's face and said, "I'm gonna f**king kill you."

The man filed a battery report and we're told he wants Bieber prosecuted and will not back down.