First of all: Don't Panic! I am not at all angry if your pronunciation is not correct. I am myself very bad at pronouncing and even at remembering names at all. If you can overlook this shortcoming of mine, I can easily, too! 🙂︎
Now that this is cleared up, lets begin with my first name: David. Try the typical english pronunciation "Day-vid" (not the in Germany common "Da-width"). I am named after my great-grandfather who might be from an area nowadays belonging to Lithuania, but fled to Germany in the 2. World War and finally gained American citizenship. Here and there is Day-vid the more typical pronunciation than the Hebrew one which – just as the name itself – became popular after the world wars in Germany. David means beloved by God and is the third most common name in the Bibel where it usually refers to the King of Israel. Most people know him from the story of the young stone-thrower David fighting against the giant Goliath.
After the for most unexpected first complication lets try my last name: Kalnischkies. The name was likely translated from "Kālnišķi" into German – and quiet literally as is spoken just like a normal German word: "Kahl-nisch-kies". I might sound Russian, but its origin is more likely from a place now located in Lithuania. I was told once that it is the job title of someone working with metal, but I am not sure that is true… The name is very uncommon in Germany, even if similar wordings are included in the counting. On the other hand, in Poland and Lithuania there seem to be cities with similar sounding names.
Kids can be cruel. It might be easy to imagine that and how my name was mangled in school. One of the nicer variants was Don Kalaschne combining the Russian AK-47 (Kalaschnikov) and my proven-by-name association with the Russian Mafia… (as a reminder, my name isn't Russian – and I am not in the Mafia).
It didn't take long before the whole school was calling me Don. Could have been worse, I guess, as the other David from my class was called Bauer (farmer) due to his last name… At the time I had to pick a nickname for this thing called Internet my uncreativity made me choose the nickname I was used to from school grounds already. I added Kult (cult) as three letters was a bit short and there are thousands of Dons on the Internet. Perhaps I picked that due to the Mafia-related films like Godfather having a good standing, but it might simple be that the first letter was K and the name still free.
I left school quiet a while ago and nobody is calling me Don anymore, but over time I grow to like it far too much as my username on the internet to change it. I am using it only on the Internet through and would like to keep it that way, so I am not going to provide any hints on how that might be pronounced.
The nickname (as well as my "normal" name) are relatively unique on the Internet, with only a few exceptions: In 2015 there was a culture festival in Lviv (Ukraine) named "DONKULT". I guess it relates to the Donbass region, but I wasn't there and have no connections where. I am using this nickname since at least 2005 myself.