Another blonde bites the dust ... Britt McHenry is OUT at the Trump White House after being caught on video throwing a drink at a fan during a heated altercation at an NBA game.

Britt was forced to resign Thursday from her job as a U.S. State Department press adviser ... according to Page Six.

She was forced out hours after we first published video of Britt throwing a drink at a fan at Wednesday night's Washington Wizards game. Video showed Britt leaving her section to a chorus of boos and blowing kisses.

Britt's pal, Andrew Fenichel, also released a video in which he discussed what went down at the Washington Wizards game ... and you gotta watch it all the way through -- because he admits he wishes he'd handled the situation better.

Britt announced her hiring to the Trump administration in September ... and she was reportedly set for a promotion ... but all that's out the window.

She previously worked as an ESPN correspondent and a Fox Nation commentator before joining Trump's State Department.

The good news for Britt ... she lasted longer than Katie Zacharia did in Trump world.