What is meaning of "pastrami sandwich"
"If you define atheism as simply “the absence of belief in God,” a newborn baby (not to mention a pastrami sandwich) qualifies as an atheist because it lacks belief in God."
It is a sandwich (two pieces of bread) filled with pastrami. The usage is quite literal in this context. If the definition of an atheist is anyone/anything who/which does not believe in a god, then not only is a newborn baby an atheist, but so is something completely inanimate, such as a pastrami sandwich.