Like Martin and Daniel I vastly prefer people to call me by my real name in real life. Unlike them, and more like David/Dave/Schwuk, I’ll tolerate people calling me “sward”, and accept that some people are really weird and just find it easier to associate with my online identity. I tolerate it because I was taught that names didn’t matter. I’m a “little squirt”, I was going to have to put up with some really stupid names that were meant to insult. All recite after me:

Sticks and stones may break my bones
but names will never hurt me.

I have been called “Swardman”, “Junior” (characterised from the film Cool Runnings), and lots of foul words. I ran with them. It doesn’t really change who I am.

What's in a name? that which we call a rose
By any other name would smell as sweet;

“Si” is an exception, I don’t like it.

If you know me through IRC there is no excuse for not knowing my real name, I do use it in IRC:

[OFTC] -!- sward [~simon@sward.bleah.co.uk]
[OFTC] -!-  ircname  : Simon Ward

[freenode] -!- sward [n=simon@fsf/member/sward]
[freenode] -!-  ircname  : Simon Ward

If you have trouble associating people with their preferred names, maybe you should configure your IRC client to display them? Of course, that does assume that people set their “realname” or equivalent appropriately.