Growing up, I had a multitude of vocal stims. When I was 7 or so, I took great pleasure in saying the word "birdseed" with an "eee" sound, a rolled "R", and a soft "D", so that it sounded like "biarrdhseed" or "beardseed" (gross approximation). I found it absolutely hilarious, to the point where it became my username and/or password of choice for a bunch of websites and online kids' games. I'd always spelled it "byrdseed", and over time, the screen name just stuck. I've never felt the urge to change it - I quite like "byrdseed". Though when I introduce myself by saying "I'm Byrd, and I like birds", it does make me feel like a cartoon character sometimes. I'm a parody of myself.
Nowadays, most people pronounce it "birdseed" with the nickname Byrd being pronounced the same as the word "bird", and I'm fine with that. Though if my seven-year-old self were to have it his way, he'd pronounce it "beard". I think it's a little silly.