Gwyneth Paltrow To Hailey Bieber, 'I F***ed Your Dad In A Bathroom,' -

DEEDS WITH DAD

Gwyneth Paltrow told a crappy joke to Hailey Bieber about sleeping with her father, Stephen Baldwin ... in a bathroom of all places, creating an awkward on-camera moment between the two.

The Oscar-winning actress appeared Wednesday on Hailey's vlog, "Who's in my Bathroom," and everything seemed normal going in.

Hailey gave a rousing introduction to Gwyneth, who walked out with a smile and warmly embraced the model.

The two sat down and began their chit-chat, and that's when things got really weird.

Gwyneth, who starred with Stephen in the 1994 film, 'Mrs. Parker and the Vicious Circle' with Hailey's dad ... referred to him as "great" and "so nice."

Hailey took the bait ... "I like hearing that. Imagine if you had some horror story. "He was terrible! It was a nightmare working with him!"'

Gwyneth then dropped the hammer ... "That would be bad. Or if I, like, f***ed your dad in the bathroom?"

Hailey tried to laugh it off, but she was visibly uncomfortable and delivered a word salad ... "I've had that happen to me actually. I don't know if he even knows that I know that. But, I've had that happen."

Gwyneth started laughing ... telegraphing it was only a joke ... "I didn't! I didn't!."

So, in the end, we ALMOST knew who was in Gwenyth's bathroom!