Because he's never spoken my actual name before.
"So, the other day Krista was - "
Silence.
A look of confusion - disgust, perhaps - spreads across his face.
"Wait a minute. Did I just say your name? I don't think I've ever called you by your name."
He then proceeds to shake it off, chalks it up to a lapse in judgment, and carries on the conversation with his friend. I shall remain "Kritta" from here on out.