Damn, Justin! We REALLY don't like what we see here ... The Biebs not only threw some major shade at his fans the other day -- he literally threw a GIFT from one of his fans, back in the girl's face!

We think this happened in Vegas after the Billboard Music Awards, when Bieber was pulling out of a parking garage and his SUV was surrounded by fans, screaming and asking for selfies. So here's what we don't get ... why the hell'd Justin roll down his window if he didn't want to engaged with his fans nicely?! We know why -- because when he's on tour, he loses his f-ing mind!!!

Justin's been photographed meditating in a park tree; he's announced a no fan-selfie rule; he posted social media messages about award shows being "hollow" and let's not forget, he pierced his nose and shaved his head. Bieber is clearly loses it every single time he goes on the road. And we kinda can't blame him -- the schedule's grueling, the demands are overwhelming, and being rich and famous is just plain difficult.

Is it too late to say sorry? Uh, yeah ...