A weak attempt at trying to portray coolness by being funny at another person's expense; typically attempted by trustafarians; often accompanied by the douche chills.
When a member of a fantasy football league insults another participant by saying in a pre-season email, "I am surprised
he even knows what football is," the rest of the league responds, "Now that's some weak shit-talking."
When people (who either have no life, are jealous, or just completely pathetic) take part in the action of stating negative, rumored, or exaggerated stories about someone else in order to make themselves in turn feel better by making the other person look worse when in actuality the person being shit talked about is most likely a better person.
Ian said to Jacob "dude, Brit is applying to a historically black college so he can get a scholarship and start a future for himself by joining ROTC and becoming one of the brave men that defend our country, how f*cking lame" I.e. Ian is shit talking
Shit talking occurs when people have too much free time (see: not having a life) and make up rumors or put down others, whether they are enemies, friends, or just randompeople.
Those shit talking scumbags just wasted a whole five minutes of my life complaining about someone who I could really give a shit less about.