Jennifer Lopez -- Nailed by Drunk Driver

JLo and Leah Remini are MADD ... because they got rear ended by a drunk driver .. TMZ has learned.

Law enforcement sources tell us .. Leah, who was driving JLo's car with the singer and 2 kids, were riding along Pacific Coast Highway in Malibu when they stopped at a light. We're told a driver in a small pickup hit them from behind and then took off.

Either JLo or Leah called 911 ... describing the driver and the pickup. Deputies raced to the scene and found the driver a short distance away, determined he was driving under the influence and arrested him for DUI and hit and run.

No apparent injuries ... but whiplash pain is often delayed by a few days.

JLo posted this Saturday ... "Sitting at a light. Riding high right before some drunk fool rear ended us in my new whip!!! Thank god everyone ok."