seriously, who says no? lol
Somebody that either:
1. Isn't interested and doesn't want to lead him on.
2. Is interested but is busy tomorrow and in the leaving confusion hears "can I call you tomorrow?" and says "no" meaning, "no...don't call me tomorrow...but DEFINITELY call me." She then later realizes what she did and feels like an idiot.
And yes, 2 happens. I have done it myself. He was really cute, too.