Bella Hadid may have had a falling out with one of her longtime friends at Paris Fashion Week this month ... 'cause eyewitnesses say the two got into an intense verbal argument -- and, they didn't leave on speaking terms.

The argument allegedly went down at a Yves Saint Laurent after-party on Tuesday, March 11 ... and, eyewitnesses tell TMZ Bella was repeatedly asking Fai Khadra to leave her alone throughout the night.

We're told Fai refused to do so and acted inappropriately toward her ... verbally berating her and raising his hands over her in an aggressive manner.

While it never got physical, our sources say it was not a friendly situation ... and, Fai verbally harassed her. People say Bella looked uncomfortable, and the two didn't leave on speaking terms.

Cops weren't called ... but, several party guests complained about Fai's behavior to top executives at YSL.

If you don't know Fai ... he's an artist and influencer with more than two million followers on Instagram. He's a close personal friend to Hailey Bieber, Kendall and Kylie Jenner, too -- but, despite speculation, he's never been romantically involved with these ladies.

We reached out to Bella and Fai about the alleged altercation ... so far, no word back.