Assuming you want a serious answer, here's the quick story.
During McDuffie's run he ran into multiple crossovers and editorial mandates about his team. Basically the only change he was allowed to make in terms of who was on the team was getting Red Tornado to leave early, and he was also forced to tie into Salvation Run, Tangent's Reign, Final Crisis, and possibly a few other events that I missed. Similarly, various events screwed up his plot lines. For example, he was planning to deal with the Per Degaton/Ultra-Humanite/Despero plot thread from Metzler's JLA run, but found out that Johns was dealing with it in Booster Gold instead. Similarly, he had to rewrite a scene when he was told the Hawks were dying in Final Crisis, and then was later told the Hawks weren't dying in Final Crisis. (It's the scene with Red Arrow and Dinah visiting what's obviously a graveyard, and that Red Arrow calls a park.)
He also had a discussion thread on the official DC message boards where people could ask him questions. Once a week to a month he'd get a question of the form "Why isn't (insert character X) on the team?" and the response would be "Editorial mandate".
By themselves, no individual comment was particularly damning (and DC knew about the thread, so they could have asked him at any time), but then various people simply took all of the comments in one big group, which came off as a condemnation of DC editorial. (It was published in "Lying in Gutters" and on scan_daily 1.0, I believe.) And then he got fired for making those comments, despite having DC editorial's permission to make that thread in the first place.