Here's some a Belgian counterjokes:

Why do the Dutch horizontal stripes on their flag
in stead of vertical? (Belgian flag has veritcals)
Because they can use it up all down to the flagpole.

Why do the Dutch have such big nostrils?
Because air is free.

There is no enmity between the Dutch and the Belgians about this. We share the fun like good neighbours and they are not seen as ethnical jokes. We have no jokes about the French, some on German, no English or other Europe country jokes.

And often enough we treat our Belgian neighbours (Helen )on a whole bag of totally free , gratis French fries . With Mayonnaise!