Mistaken Identity

Tonight I went to the grocery store to pick up a few things (side note: I like grocery shopping at night because it's always so much less crowded). As the checker was scanning my items, a guy walked up behind me... he looked about 23 years old. Out of nowhere he says "oh god!" in a very disapproving way. I looked at him to see what he was talking about and I noticed him looking at me. I gave him a small grin... his response was sighing loudly and rolling his eyes. I was definitely caught off guard and didn't know what he had against me seeing as we were almost done checking out, so I just continued to pay and tried not to think about it.

Then he says loudly, "I hated you in high school."
I looked at him trying to figure out who he was. I didn't know him... I went to high school 2000 miles away. So I say, "what?" to be sure I heard him correctly.
"I hated you in high school," he says even louder without looking at me.
Pause. The checker looks at me as if I should respond.
As I gathered my bags I say, "I'm sure you are justified in your hate toward the girl you think that I am, however, I went to high school in Texas and graduated at least 4 years before you."
He looked at me and his face turned bright red. "I'm so sorry. Oh my gosh... I completely thought you were someone else. I'm so sorry."
I smiled and told him not to worry about it. As I walked off I heard the checker say, "that was probably the funniest thing I've ever witnessed in this job."

I don't know who the girl is he apparently still hates so much, but I think it would be funny to witness the interaction that would take place if he really did run into her. Poor guy... there was a lot of built up hostility there.