Deriving from the word malakia (to jerk off) it is mainly used in other contexts such as, addressing a friend. In Greece it is the vague equivallent of the word "nigger" between afro-americans, in that it can be used freely among friends but never from an outsider.
ela re malaka, ti les tora (c'mon malaka are u kidding) - friendly
telika eisai poly malakas! (I came to realize that u r a malakas after all) -not friendly