Something wicked was going down outside of One Sunset last night -- A couple of girls got into a shouting match, when one girl decided to haul off and bitch-slap a blonde.

But she messed with the wrong non-tourage, because the girl was with David Weintraub (memba him from Sons of Hollywood? Yeah, didn't think so.)

After screaming at the other girl, she was eventually subdued by the bouncers and walked off...alone. So sad.

Shauna Sand was also seen standing outside of One Sunset, but miraculously, she wasn't the strangest thing going on that night.

Also...