I'm not sure you can craft a very specific, very brief definition of 'fan' versus 'stalker'. After all the word 'fan' comes from the word 'fanatic.'
And I have to disagree that this thread is funny. I don't find it funny in any way, nor would Taye Diggs and his wife, I'd imagine.
What I can say is that everyone's behavior is a little different and the specific way in which they choose to express their respect or admiration probably makes it easier to define whether they have crossed the line.
For example, a true fan, that is a person who respects the person's work and their privacy, might on a given day choose to approach the actor and express their thanks for a job well done or for some piece of work the person has done that has touched them. The reason they will decide to approach the actor is because the actor doesn't seem busy, preoccupied or tired and isn't engaged in some private activity like having dinner with another person. In other words, a fan can tell the difference between appropriate and inappropriate behavior and timing.
Whereas a stalker sees the opportunity, no matter when it presents itself, and seizes it every time because they feel they have the right to do so or because they either hate or love the person enough to NEED the interaction. Regardless of whether their behavior frightens or makes the actor uncomfortable, the stalker is oblivious, because she/he lives in another reality where perhaps they have already imagined a sexual relationship, a love affair or a friendship and it is very real to them.
Or, if they haven't imagined that relationship, they are determined to get the actor's attention in order to engender a relationship because they believe they were MEANT to be together or to be close in some way. If the person hates the actor for some imagined affront, the opposite applies and the stalker believes that it is his or her mission to harm or kill the actor or celebrity. Ask David Letterman about the woman who kept showing up at his house in CT. Ask Yoko Ono about the man who murdered John Lennon.
Sometimes stalkers can seem harmless. But even if they don't mean any harm to the actor, they are not doing themselves any favors by living in a dream world. They'd be better served to get a life and a therapist and move back into the real world with the rest of us.
"Always smile at your enemies. It will keep them on their toes"