I hear ya, Brian... on my first birthday card, my grandmother misspelled my name as "Brain," and it's been happening ever since.
In fact, in happens so often that my nickname is Brain.
(Oddly enough, my other nickname is Sammy... which was my grandfather's name, and is my uncle's name. People around our town, as well as Great-Aunts & Uncles, etc., have always called me Sammy because of my resemblence to my grandfather and uncle. Sometimes I'm more likely to answer to Sammy, than I am to Brian! *lol*)
To be honest with you, it doesn't bother me when someone misspells Brian. In fact I usually get a pretty good chuckle out of it.
And I'm sure it has happened to every single Brian, at least once.
Heck, on one episode of the animated series Family Guy, their dog, who was also named Brian, was entered into a dog show, and his name was misspelled as "Brain" on the scoreboard.
Johnny Stew