I'm not being facetious. I really want to hear everyone else's stories of truly scary anime fans.
And as forum etiquette dictates, I'll go first:
Mine was at a Vulkon convention about three years ago. I met a fellow anime fan while browsing one of the fansub tables in the dealer room. We exchanged phone numbers, and ended up going to MegaCon together. After that, he got scary. He assumed I was his girlfriend when I NEVER gave any indication of that, spoken or otherwise. It got to the point where he started showing up at the computer lab on campus during the week and surprising me. I probably should've called security or something, but as he wasn't making any threats there wasn't much I could do. I figured when the year was up, I'd be changing rooms and phone number at the apartment complex I was at anyway.
It half-worked. I ran into him at the anime club's local convention that summer. Worst time I ever had at a Con, 'cause I spent the entire day trying to avoid him. And they had showed Princess Mononoke that Saturday, but I missed it because I was hiding from the crazy stalker fanboy

I don't know if this had anything to do with it, but I was 18 and he was 17. However, I was in college while he was still in high school. I honestly can't tell you why he followed me around like a second shadow, either. I'm no prize (I'm the one on the left).
Now it's your turn. Give me some scary fanboy.girl encounters