Just trying to relate to his people.
Check it out:
Recently, Barack Obama — a Demosthenes determined to elevate our politics from coarseness to elegance; a Pericles sent to ameliorate our rhetorical impoverishment — spoke at the University of Michigan. He came to that very friendly venue — in 2012, he received 67 percent of the vote in Ann Arbor’s county — after visiting a local sandwich shop, where a muse must have whispered in the presidential ear. Rep. Paul Ryan (R-Wis.) had recently released his budget, so Obama expressed his disapproval by calling it, for the benefit of his academic audience, a “meanwich” and a “stinkburger.”
Try to imagine Franklin Roosevelt or Dwight Eisenhower or John Kennedy or Ronald Reagan talking like that. It is unimaginable that those grown-ups would resort to japes that fourth-graders would not consider sufficiently clever for use on a playground.