Richard Sherman's post-game interview was epic, but it definitely wasn't shocking, especially if you've been following him—he's only been in the league for three years, so there's not too much ground to cover. Sherman has talked so much trash that it's an achievement his on-field skills and accomplishments aren't completely covered by his hubris.
That said, his mouth has always been a large part of his public persona. It's grating to some but hilarious to many others. Take the above video for example, where he hits Bourbon Street in 2013 to ask people who's better: Richard Sherman or Darrelle Revis. It's hard to tell what's funnier: Sherman overacting when an old man disses him without knowing he's actually talking to Richard Sherman in the flesh, or the dude who interpreted Sherman as Dreadlock Jesus.
Below is NFL's Sound FX catching Sherman's eccentricities off of the field. It also covers that time he got mushed by Redskins' Trent Williams...and still talked some more shit. Because Richard Sherman isn't scared, and he'll keep Shermaning by any means.
Next is the most likeable—and until now infamous—example of Sherman's trash-talk. Only Skip Bayless getting owned on his own television show can make Sherman look universally likable.
Lastly, Sherman cracks some jokes with his family member (Sherman didn't have much of a choice when he said "my beard look cute"). Sherman's outspokenness isn't an act.