Ethan Shanfeld Half an hour into “Songs About Fucking,” James Gallagher’s music documentary premiering at Tribeca on Saturday, Marc Rebillet points the microphone at a burly, bearded gentleman standing in the front row of his concert and asks, “Sir, how are you?” “I’m great,” says the man, dressed in only his underwear and a bathrobe. “I’m pregnant and it’s yours.” “I didn’t expect you to be here, if I’m being honest,” replies Rebillet, also robe-clad, weighing his options. “You wanna come up here and deliver this baby?” Rebillet then invites three women — one of them actually carrying a child — up onstage to assist with the procedure, before the so-called pregnant man grabs the mic and starts rapping over a techno beat. Then, he sits down so Rebillet can thrust himself from between his legs — an infant, crying on the floor.