Obviously the standard is right handed mouse. I just can't understand why a lefty would ask for a left handed mouse. I mean, is using a mouse that dextrously demanding that you would need a left handed mouse to compensate for your inability to use your right hand to click a button?
If that were the case, I would need a keyboard that had all the keys on the right side, because it's more dextrously demanding to type than it is to click a mouse.