I remember the first "bad" turbulence I experienced was flying over Afghanistan from Thailand I think in 2006. It was non stop for about 2 hours and the plane was shaking a lot. Been on probably ~100 flights since then, with some that had much worse turbulence, but you get used to it. It can still make your stomach go a bit queasy though! The worst I've ever experienced was in an ATR-72 flying from Boracay to Manila, just after a tropical storm had past.