Justin Bieber -- Segway-Riding, Pot-Smoking, Nightmare Neighbor -- Allegedly

Justin Bieber is hell on wheels, and not just in his Ferrari -- neighbors tell us they saw him over the long weekend riding a Segway and smoking a joint ... smack in front of neighborhood kids.

Multiple neighbors in the exclusive, gated Calabasas community say Bieber and his friends have turned the neighborhood upside down. We're told they've called cops twice in the last five days over excruciatingly loud noise coming from Bieber's house where parties were going full-bore at 3 AM.

Neighbors tell us Justin has been a real problem in his Ferrari and on his motorcycle. Aside from the incident Monday night when he was allegedly roaring through the neighborhood, we're told Justin frequently drives recklessly. Residents say Justin almost struck a neighbor pulling out of his driveway Sunday.

As for the Segway incident, neighbors say on Sunday Justin was riding side by side with a buddy, who was also smoking a joint on his Segway.

Neighbors tell us the homeowner's board is planning on taking action -- for starters, they've talked to cops who promise they will begin towing vehicles that are left on the street overnight -- a frequent occurrence when Bieber or his friends throw parties.