Basically it has been known for a while that JBL is kind of a dickhead and was constantly playing "big man on campus" during his active career. This includes one incident where during a big melee in the ring at ECW One Night Stand 2005 he beat up The Blue Meanie for real, causing him to suffer a head wound that needed 12 stitches to close.
Recently professional wrestler Justin Roberts published his autobiography. In it he accuses JBL of all sorts of bullying and hazing, e.g. just throwing the luggage of other wrestlers down the street or forcing people to join the heel bus even when they are faces so they remain within JBLs grasp. He also accuses JBL of stealing Robert's passport during a european tour, causing him all sorts of trouble. Wrestlers John Morrison (now Johnny Mundo in Lucha Underground) and Joey Mercury confirmed in interviews that they were involved. They were themselves bullied by JBL and were supposed to steal the passport, but both said they didn't do it. Meanwhile JBL's response to Roberts was, and this is a quote from twitter: "I didn't take Justin Roberts passport ... he was hated by the whole crew. He's an idiot." Which is, you know, the kind of thing a bully would say.
Almost at the same time it was revealed the the recent departure of Mauro Ranallo from WWE and the Smackdown commentary team specifically was because of bullying by JBL, including statements to the effect of "You don't deserve this and nobody cares" when Mauro won an award for his commentary. Ranallo also suffers from clinical depression, a fact known to the entire locker-room which makes things all kinds of worse.
This whole thing now has also been picked up by several large publications that don't cover Wrestling specifially, like Sports Illustrated and Deadspin. Meanwhile Dave Meltzer, the most respected reporter in the wrestling business, has deeemed this to be a natural outgrowth of the WWE corporate culture and Vince McMahon's personality specifically. Meltzer said that in any other company JBL would have been fired a long time ago. Also notable is that CM Punk during his infamous Pipebomb promo was cut off right before launching into a rant over the WWE's hypocrisy in supporting an anti-bullying campaign.