From a New York Times piece on the reasons the HPV vaccine would — or would not — be given to boys:

Baruch Fischhoff, a professor of decision sciences at Carnegie Mellon, thinks that older boys may see a mix of benefits in Gardasil. Being able to say to a girl, casually, that you had the shots, boys might think, If I can slip that into the conversation, it makes me less of a risk and seem like more of a humanitarian, Dr. Fischhoff said. So the self-interested and altruistic motives could actually support each other.

-Greg Dahlmann

Earlier on blog.bioethics.net:
+ Men and HPV