"Our next roaster, Anthony Jeselnik, is here because Greg Giraldo is dead," announces host Seth MacFarlane, bringing the relatively unknown comedian to the stage. Of the comics and celebrities gathered to roast Donald Trump, Jeselnik is the least famous—a fact he is reminded of constantly throughout the evening.

But to the surprise of his fellow comedians, Jeselnik kills. He slays with vile, rapid-fire bursts. Punchlines pop every 30 seconds—set up, knock down, set up, knock down. His safe good looks belie a twisted stage persona: he is arrogant, condescending, relentlessly clever, and hideously dark.

"Donald," Jeselnik says, addressing the guest of honor, "I'm not even sure you're aware of this, but the only difference between you and Michael Douglas from the movie Wall Street is that no one's going to be sad when you get cancer." The ensuing gasp is the biggest any performer gets all night. Still, the audience cannot suppress their laughter, try as they might.

At last month's Comedy Central roast of Charlie Sheen, Jeselnik continued the coming-out party, cracking to Sheen: "The only reason you ever got on TV in the first place is because God hates Michael J. Fox."

"There is no line whatsoever," Jeselnik said to Marc Maron on a recent episode of the WTF podcast. "Those things that you're not supposed to say are exactly what comedians are supposed to say. I think anyone who questions that is dead wrong."

But Jeselnik isn't aiming low in the Howard Stern, dirtbag sense. Instead, he's competing with himself in concise, traditional joke writing: lead the audience somewhere and surprise them with a twist. He's trying to make jokes so good that audiences laugh despite the rancid tenor.

Off stage, Jeselnik cut his teeth as a writer for Jimmy Fallon, where he wrote a minimum of 100 jokes each day. This stint fed Jeselnik's economy and rapid-fire style: He's a joke-writing machine. "To [your] brain it's like math," Maron said to Jeselnik in their interview.

I asked Jeselnik about the comment and he colored his talent differently. "The language is way too complex to just call it math," Jeselnik says of joke writing. "Maybe 'chemistry' or 'black magic' would be better. I just love jokes. I love trying to surprise people when they know it's coming anyway."