START A CROWD SINGALONG WAITING FOR THE TRAIN AFTER A SHOW AT RADIO CITY

Nothing creates a transitory flash community like an impulse singsong, turning a clutch of sweaty, grumpy strangers into an angelic choir. Someone needs to get it started; so let that someone be you. Pick a banger by the artist you all just saw together. And if that fails, go with Queen’s “Bohemian Rhapsody.” It won’t be long before the subway walls are echoing with Galileos and magnificos.