I learned the legendary "Donaudampfschiffahrtsgesellschaftskapitän" at school, but of course you can lengthen that by simply adding the word "widow" to it and then further extend it by adding "dog" to get the Danube steam ship company captain's widow's dog. But then you could add "collar" or "flea" etc. There is no end to this highly entertaining German sense of humour (or is it a sport?).
But then I found this:-
Donaudampfschiffahrtselektrizitätenhauptbetriebswerkbauunterbeamtengesellschaft
A work of sheer genius.
If you want to look up each word to get the jist, here it is split up.
Donau dampf schiff fahrts elektrizitäten haupt betriebswerk bau unterbeamten gesellschaft
