The worst I've had was a very long time ago - you can tell, it was on PanAm flying into Berlin. Not only were we in a thunderstorm - bright flashes and a noise like a bucketful of small stones thrown against the hull, which I assume were lightning strikes - but the CC were strapped in and one of them was trying to use the barf bag without anyone noticing....
I found it interesting rather than frightening, but the aircraft was jumping around more than a little bit.
The other time was wake turbulence on a Bristol to Paris flight as we got to the French coast. The four of us drinking champagne didn't spill a drop, but three people drinking coffee had a small bath in it......There's a moral in that somewhere!
Back in the mid 1980's, there was an article in Flight that said some 60 people a year were injured by turbulence on the North Atlantic route because they weren't strapped in. Since reading that, I only unbelt to go to the lavatory...