That's about the worst faux pas you can make with the Flemish, besides generalizing them as "Belgian" and assuming they all speak French.
I'm not Dutch dammit
Gah... I admit it, I always confuse who's Dutch and who's Flemish, I'm as bad as those that are confused whether I'm English or Irish... I've turned into my worst nightmare! * grabs knife *
* peels apple *
Its a bad habit I got from hanging around with a nationalistic (but vegetarian) Dutch friend I have who believes Belgium should just be split between France and The Netherlands anyway...
It must be the second worst faux pas though, I would presume anyone would hate being called French twenty times more then Dutch.