Along with the scripted clapping and the heroes sitting in the First Lady's box, a stoic and straight-faced Supreme Court is one of the conventions of the State of the Union. That's why people seem so shocked at Samuel Alito's demonstrative response (for a Supreme Court Justice at least) to President Obama's criticism of the Court's recent ruling on campaign finance. As Obama blamed the court for "open[ing] the floodgates for special interests, including foreign corporations, to spend without limit in our elections," Alito grimaced, shook his head and mouthed the words "not true." Coming from a Supreme Court Justice, this is basically the equivalent of Joe Wilson putting the president in a full nelson.
Justice Alito's 'You lie' moment? [Politico]