I would guess (but not bet money) that it was someone from
EveryDevel or Blockstackers, and not a perl monk -- since
technically, the shirts aren't really available (where's
that web store? *hint hint*). I picked one
up at lwce, I know at least one or two other monks did as well.
As a sort-of follow-up, I was wearing my PM shirt at a
recent event and someone came up to me who actually knew
what the site was. He wasn't a perl monk either -- which
confused me greatly. My worldview does not include the scenario
in which a person knows of PM and is not a registered user and
regular visitor. It turned out that he was a friend of Chris
diBona (visible in the random monk pic rotation). Minor
mystery solved.
e-mail neshura