My nickname is a bit of a long story (which I'm sure I've told before). Many years ago, my friends started calling me "rbp", which are my initials and my username on most systems (whenever I can snatch it). When I met my now wife, her then 11-year-old niece questioned why my nickname would be longer than my name (I'm Brazilian, and in Portuguese "rbp" is pronounced with four syllables, whereas my name, "Rodrigo", has 3). So she started calling me just "r" ("Érre", in Portuguese - 2 syllables). Everyone loved it (myself included), and my friends quickly took to calling me "r".
Many years later (in fact, five and a half years ago), my wife and I moved to the Netherlands. There, to try and get people to be able to pronounce my nickname, I started spelling it phonetically in Dutch, "echie". It added to the coolness factor that "echie" is a (somewhat childish) way of saying "Really!".
All of which of course gets lost on anglophone audiences, since I can't think of a phonetic way to explain the pronunciation of "Érre", "echie" in English
My avatar is just me, clowning around in Munich :^)