-San is generally polite. Sans -San means ... either rudeness or close friends, depending on the context.
-Chan is affection, usually towards girls (If you were addressing someone as "Little Suzie," and meant it as a compliment). As such, -Chan towards boys happens, but is giggle-worthy or an intended insult.
-Kun is a term of affection towards a boy who is a close friend, usually from a girl, but not always. It is also very hard to get away with properly, or so I've been told.
In addition, -Sama is a clear-cut better ("My Lord"), or flattery.
^ My limited scholarly experience. I have no actual speaking experience, so I may be very wrong.
no subject
-Chan is affection, usually towards girls (If you were addressing someone as "Little Suzie," and meant it as a compliment). As such, -Chan towards boys happens, but is giggle-worthy or an intended insult.
-Kun is a term of affection towards a boy who is a close friend, usually from a girl, but not always. It is also very hard to get away with properly, or so I've been told.
In addition, -Sama is a clear-cut better ("My Lord"), or flattery.
^ My limited scholarly experience. I have no actual speaking experience, so I may be very wrong.