When I was four or five years old I remember seeing a semi-truck crashed into Mel's Diner. How did it happen?

That was a very cool episode. Flo is jealous of her boyfriend's new truck driving partner (a female), so she decides to get Alice to teach her how to drive a semi. She's doing really well until she hits the gas instead of the break and goes sailing in through the front of Mel's Diner as Mel and the others have to run and "Hit The Deck!!!" This was one of the final episodes with Flo before she left, I believe.