I fly a light single, albeit a rather large and not so light single and the worst I experienced was a massive wing drop in turbulence. It was like a giant grabbed the wing and pulled it down. But it was never even close to being flipped over. It was easy to recover from. Even for light aircraft it would take something like hitting the wake turbulence of a heavy to flip over and even then you'd have to be really unlucky.
When it comes to airliners, short of flying into the heart of fully developed thunderstorm somewhere in the tropics then it just woudn't happen.