The conversation(and the girl) was obviously was on his mind. Your best bet is to ask him.
it can...but it can also just mean that she is really chatty and easy to have a conversation with :)
It obviously depends on what she is saying.
good morning fat girl
that she might like you or she wants to be friends
It seems to mean a lot of things. Here are a couple parts of the conversation where the possible meanings are explained. "Good morning!" said Bilbo, and he meant it. "What do you mean?" Gandalf said. "Do you wish me a good morning, or mean that it is a good morning whether I want it not; or that you feel good this morning; or that it is morning to be good on?" . . . "What a lot of things you do use Good morning for!" said Gandalf. "Now you mean that you want to get rid of me, and that it won't be good till I move off."
You are starting to like her
if the girl and your sibling are the same age or the girl is younger, it could mean that the girl wants to get to know you to get closer to your sibling. If your sibling is a girl it could mean she idolizes her or something like that, (or shes a lesbian and the same as above) Otherwise she could just be making conversation hope this helps :)
If a girl bumps into you, it could just be an accident or it could mean that she's looking for an excuse to make conversation with you.
Yes.
if she always trys to make conversation with you it means that she really likes you so therefore wants to talk to you and if she smiles it means she's happy to be with you
It means she saw you, she is using a reason to bring up conversation with you. She's friendly.
If you want to be mean, join in their conversation. Or, you could just smile at the guy and walk on by.