Brock Lesnar had a huge blow up backstage after WWE Extreme Rules according to F4Wonline.com.
Lesnar was reportedly told leading up to the WWE Extreme Rules event that the plan for the pay-per-view was going to see Cena leaving on a stretcher, totally incapacitated and injured off television at the hands of Lesnar. Obviously, this didn't happen. Cena went over in the match, made a speech and walked out on his own power.
Backstage Lesnar apparently made a huge scene as he was upset at Cena's post-match speech. He felt WWE officials had double crossed him to make Cena look good and Lesnar weak. According to reports Lesnar was tearing things up and flipped out on Marc Carano who is the assistant to John Laurinaitis. Lesnar went on about how things were a mess in WWE.
There is speculation that some or all of Lesnar's backstage tantrum was orchestrated by Lesnar and top WWE officials to work the rest of the roster. There is also speculation according to the report that Lesnar causing a scene backstage was mostly his way of letting everyone know he isn't afraid to quit and doesn't need WWE. Some feeling Lesnar really didn't care as much about the change in booking but wanted to show off his situation of not needing to be there.
Reports also say Lesnar suggested Cena pulled the top rope down when he was standing on the apron which caused Lesnar to fall out of the ring and almost blowing his knee on that spot during their match.
Where Lesnar goes next in storylines is up in the air in WWE which is why Lesnar had the walk out moment on RAW last night to help buy some time and figure out what to do next.