Justin Bieber Yells at Teenagers Harassing Him in Beverly Hills

Justin Bieber 's definitely all grown up and sounding more like Clint Eastwood than a young pop star when some teens in Bev Hills ticked him off in a fancy hotel.

The new clip circulating on social media shows the singer-songwriter Thursday in the lobby of the Waldorf Astoria, a popular celeb hot spot, where he confronted the pack of teenagers.

In the vid, he's angrily asking the teens what they find so funny -- very Joe Pesci from "Goodfellas," we gotta say -- waving them away from him while hotel staff appears to be shooing them out the door.

Witnesses tell TMZ he had good reason to be upset ... he was meeting his pregnant wife Hailey Bieber for lunch at the hotel when 8 teens -- who were at the hotel for a bar mitzvah -- started following him around and yelling at him.

Bieber had limited security and asked the kids nicely to back off at first ... but, they kept filming him like a circus animal, we're told -- and JB got frustrated.

Our sources say Bieber didn't swear at the kids, and he was just trying to get on with his day ... and, we're told he was just worried about his wife's safety.

As you know ... Justin and his wife Hailey are expecting their first child any day now. Sources told us she was six months pregnant in early May. Do the math ... we can expect Baby Bieber very soon.

HAILEY BIEBER'S PREGNANT PICS

Click Image to Open Gallery

Justin shared a loved-up snap with his better half recently ... featuring Hailey's huge baby bump -- so, clearly, everything's going great in their relationship.

That said, Bieber's not a baby, baby, baby anymore -- so, message to all you young whipper snappers ... don't test this daddy-to-be!