Hmmmm... I dont think I can really give any sort of story like these, as I am mostly ignored by those around me, so I dont have any real stories I can tell about people mistaking me for stuff.
The only plausible reason I can think of, is that people may be too intimidated to speak to me, because I wont say anything unless somebody speaks to me first (Barring the odd thing that I may blurt out, such as hearing somebody talking about a certian game, and then me blurting out the solution that they are stuck on).
It might also be because I tend to be stone faced, and walk twice as fast as everybody around me. Then again, I also dont tend to care about my appearance, and I tend to have some odd mannerisms.
Edit: By stone faced, I mean I wear a blank expression and often speak in monotone.