Definitions by Tadukhipa

kun 

a suffix attached to the surname of younger men or the same age as the speaker.
it isn't used between women or addressing superiors however a man can address a inferior woman by ~kun (in schools or companies)
it is less polie than ~san.

(35)Takenouchi: doomo Daigo~kun
(25)Daigo: doo itashimashite Takenouchi~san

kun by Tadukhipa December 29, 2005