Lisa Vanderpump's hubby Ken escaped the long arm of the law this week -- when he was pulled over by a cop in West Hollywood ... for something that probably WASN'T EVEN HIS FAULT!!!

Here's the deal -- sources tell us an eagle-eyed cop spotted Ken's fancy Bentley cruising down Santa Monica Blvd. at nighttime WITHOUT his headlights on.

But here's the rub ... we're told Ken had just picked up Lisa from their restaurant SUR ... and we're guessing that's where things went wrong.

WHY? Because he probably left the car with the valet ... and sometimes valets TURN OFF YOUR HEADLIGHTS (even if they're set to automatic) ... and it drives us frickin' CRAZY!!!!

Anywho ... Ken didn't get in trouble for the headlight issue, the cop let him drive off without a ticket.

We can't confirm the valet thing either ... but c'mon, you KNOW it's happened to you.