Oh, I know that one -- IIRC some people in India think if you eat melons, watermelon, or cucumbers or other water-heavy fruit, and then drink water, that's too much water for your system to handle and it will give you indigestion, maybe diarrhea, and chill your stomach. Definite food taboo thing. There was a similar thing with cucumbers and indigestion when I lived in Italy, they were supposed to give you gas.

You might like this article: Don't Eat the Cucumbers, and Other Food Rules

I'm sure my grandma rattled off a lot of Hungarian food taboos to me, but I hated her cooking so I never took them that seriously.