Jian ren is a term to define a kind of despicable people who are always willing to laugh at someone or show off themselves, and snobish, mean, uncomely, roguish... basiclly, Jian ren is a combanition of all bad personalities.
But sometimes to call someone esp. between friends is just for kidding.
1.George is a Jian ren, he beat a little boy and pushed him into a wallow.
2."Hey,Jian ren, how are you doing?"
"I am fine, Sha bi!"