Car started vibrating terribly after starting it up late last night at the grocery store

Had it towed from the lot to the mechanic today. No idea what's wrong.
... Then I watched this French woman have an epic meltdown in the car rental place because they gave her the Camry she reserved and not an upgraded SUV that she actually wanted.
Then, as the customer behind her, I got handed the keys to an SUV since that's what I booked and she didn't like that one bit.
It reminded me that it's a good thing I don't have a business that deals with the general public, cuz I'd eject those turds so fast...