I agree with TOGABOY with the bay of bengal being one of the worst areas. I've never flown through that area without some very lumpy weather especially towards the western side near RGN or Nicobar islands. It is not unusual to see banks of thunderstorms hundreds of miles wide, their tops being well over FL400, other times there are just a few CBs but they are pretty impressive. Nevertheless lumps and bumps aplenty.
Last year we had one particular episode for over 30 minutes, and that was after we had plotted our way around the worst of it. The cabin crew reported nearly every call light on for extra sick bags. The aircraft behind (QR I think) declared a medical emergency due to a woman going into prem labour. We spent the next 15 mins on RT relay just so he could divert to BKK.