Kun is used with people you consider to be your best friend.
I win because violence is never the answer...
I think it can be changed depending on the person. "San" is only for general respect while the other two is for a friend or 'kun' can be used for someone in a workplace who is newer.Huh, the entire time I thought it was:
-chan = girl
-kun = boy
-san = surname
I win because now I'm confused. @_@