Have you wondered what it is, in the 21st century, that makes a man a man? Morgan Spurlock’s new documentary “Mansome” tackles just this question.

Spurlock, who received an Oscar nomination for 2004’s “Supersize Me,” gathers together a star-studded cast to help him examine modern masculinity. Celebrities like Judd Apatow and Paul Rudd take up the question with varying degrees of humor and humility. Grooming, fashion, and body image are chief among the topics explored. Spurlock also interviews competitive ‘beardsmen,’ professional wrestlers, and everyday men and women in search of the Holy Grail, er, Holy Male that is.

While “Mansome” does have moments of genuine hilarity (John Waters ponders retiring from moviemaking by shaving off his iconic moustache and eating it in front of a live audience), in the end it’s too thin and shortsighted to be truly engaging. But Will Arnett and Jason Bateman debating masculinity during a men’s spa day, complete with facials and pedicures, is almost entertaining enough to make it worth the video rental fee.