At 35, Martin O'Brien has already outlived his life expectancy. And in performances in which he attaches pegs to his testicles or smears himself with mucus, he brutally confronts his mortality It's not often you meet someone who self-identifies as a zombie. Are your pronouns he, she, they " or it, I ask. "Let's go with 'it'!" laughs Martin O'Brien, the most jovial zombie you could hope to meet. He (the pronoun he act…