There are precisely two complex ideas in Peter Sinn Nachtreib’s boom! — now at Jobsite Theater — and once we’ve fully understood each, there’s very little to hold our attention. Idea number one is that the earth is about to be hit by a comet (thus the title), and the regeneration of the human race will depend upon the gay man and baby-hating woman on the stage in front of us. Idea number two is that the duet we are witnessing is a kind of museum exhibit, more or less stage-managed by a third character who stands on a walkway above the action, plays a drum to affect the actors, and at times addresses the audience directly. Each of these concepts is rich enough to develop into an evening of wild theater, but