Oops!!

A man standing in line at a check-out counter of a grocery store was very surprised when an attractive woman behind him said, "Hello!"
Her face was beaming. He gave her that "who-are-you?" look and couldn't remember ever having seen her before. Then, noticing his look, she figured she had made a mistake and apologized.
"Look," she said, "I'm really sorry, but when I first saw you, I thought you were the father of one of my children," and walked out of the store.
The guy was dumbfounded and thought to himself, what the heck is the world coming to? Here is an attractive woman who can't keep track of who fathers her children! Then he got a little panicky. I don't remember her, he thought, but, MAYBE... during one of the wild parties I went to when I was in college... perhaps I DID father her child! He ran from the store and caught her in the parking lot and asked, "Are you the girl I met at a party in college, and then we got really drunk and had wild crazy sex on the pool table in front of everyone?"
"No!" the woman said, with a horrified look on her face. "I'm your son's second-grade teacher."