Kind of like "You lie", but kinder, gentler
via Washington Post;
Obama took issue with a ruling that overturned two of the court's precedents and upended decades of restrictions on corporations being able to use their profits to finance campaigns for and against candidates.
It proved to be a striking State of the Union moment: With six justices seated in their black robes directly in front of him in the House chamber, Obama said: "With all due deference to separation of powers, last week the Supreme Court reversed a century of law that, I believe, will open the floodgates for special interests, including foreign corporations, to spend without limit in our elections."
As Democrats applauded, cameras showed the justices sitting expressionless. Except Alito.
"Not true, not true," he appeared to say, as he shook his head.
Also possible that Alito was actually disagreeing with the details as Obama laid them out;
...Justice Alito shook his head as if to rebut the president’s characterization of the Citizens United decision, and seemed to mouth the words “not true.” Indeed, Mr. Obama’s description of the holding of the case was imprecise. He said the court had “reversed a century of law.”
Either way, I'm sure Democrats will have no problem finding "evil corporations" to donate to their campaigns, no doubt in the hope that they'll be eaten last.