John Mulaney got the sweetest birthday surprise Friday night.The comedian, who is currently on the road, touring his latest stand-up sets across the country, got the ultimate 40th birthday gift when Olivia Munn and their nine-month-old son, Malcolm, surprised him at his tour stop in Nashville, Tennessee Friday. Both Munn and Mulaney took to Instagram to share pics from the funny man's on-stage birthday celebration, which included balloons, cake and a «Happy Birthday» serenade from Malcolm himself.«Malcom surprised John on stage last night to sing HBD with the whole audience,» Munn wrote over a photo of a visibly stunned Mulaney, who appeared to gasp when seeing Munn and his baby boy step on stage.Munn also shared shots of Mulaney and Malcolm enjoying dad's birthday festivities once the crowd had cleared.