"He could do the walk, the strut, the face, and act out the dramatic scene of the Rolling Stones onstage at the Altamont Speedway outside Livermore, California, on December 6, 1969, as violence that would lead to murder broke out in the crowd below: 'Hey, hey people, sisters and brothers, brothers and sisters, come on now! That means everybody just cool out! They’re fightin’ a lot. Will you cool out, everybody?'"
Page 341 of "Barack Obama: The Story," by David Maraniss.
The line I remember from that scene is "Who's fighting and what for?" Here's a good on-line clip of the Speedway incident, taken from the excellent Maysles Brothers documentary "Gimme Shelter."
It's interesting to think of Barack Obama seeing himself in the Mick Jagger role. It's not just that Obama envisions himself as the rock star, but that he saw the partying dorm-mates as the rough crowd at the Speedway who needed instruction from the stage on how to cool out.