Bargoens, The Slang From Amsterdam
Dutch is all but a uniform language. The many regional variants can differ greatly from each other. Even so much that people cannot understand each other very well when using different dialects. Several years ago, a friend and I were travelling from our hometown in the east to the south of the Netherlands. We shared a train compartment with two elderly ladies who were submerged in a lively conversation.
The whole trip we tried to make out what language they were speaking, and even though we both have a linguistic background, we could not make sense of it. When at a certain point one of the ladies asked us, with a heavy southern accent, whether this was the train station of Eindhoven, it finally dawned on us that we had been listening to a southern Dutch dialect all the time.
One of the most interesting Dutch language variants is Bargoens. This is the slang of the old inner city of Amsterdam. It used to be a secret language used by criminals, but over time it became common in the poorer parts of the city, and certain words even ended up being used (or at least understood) nationwide. Since for a long time Jewish people were overrepresented among the poor, Hebrew and Yiddish have heavily influenced Bargoens.
My first contact with Bargoens was during a student job I had in a cell phone shop. On my first working day, the manager (from Amsterdam) said to me "Hé muts, zet die meuk eens weg.". To my mind, he literally said: "Hey, hat , put that (unknown word) away.". This request was a complete mystery to me. Originally, I am from the eastern part of the country where "muts" just means "hat". Calling a woman a hat seemed very odd to me, and I had really no idea what he meant with "meuk". I had never heard that word before.
Later I asked my then boyfriend, who was from Amsterdam, what those words meant. He started laughing and explained that "muts" is slang for the female organ and is used in extension for women. More specifically, for women who are not so bright. The word "meuk" also is western slang meaning "trash". Although I have seen language that is more refined in my life, I did find it entertaining in a way.
Personally, I think that is exactly the reason why Bargoens is the best known dialect to any of the Dutch: it tends to be funny, shockingly blunt or both. Some examples to give you an idea (unavoidably including some strong language):
Rijkshotel: lit. "government hotel", meaning jail.
Lulletje Rozenwater: lit. "prick rose water", meaning a dork.
Villa Duinzicht: lit. "villa dune sight", meaning jail (an infamous jail in Scheveningen was near the sea).
Gratenpakhuis: lit. "bone warehouse", meaning a very skinny person.
Jan met de pet: lit. "John with the cap", meaning ordinary or plain people.
Potloodventer: lit. "pencil salesman", meaning an exhibitionist.
Tot in de pruimentijd: lit. "see you in prune time", meaning see you later.
Spijkerbak: lit. "box of nails", meaning an old car.
Kip: lit. "chicken", meaning a policeman.
Mierenneuker: lit. "ant f*cker", meaning a quibbler.
So if your ancestors came from Amsterdam and did not belong to the upper classes, it is very likely that they spoke or at least understood Bargoens. If you want to know what it sounds like, listen to this Amsterdam dialect fragment collected by the Meertens Institute. To compare it with standard Dutch you can watch this fragment of the Dutch News.