It really does seem ridculously common for old men (not just martial arts masters) to have dirty minds in anime. Then again, it seems common for younger characters, too, but it seems like the older characters are the worst offenders (at least from what I've seen).
Anyway, of COURSE Greg is ashamed that he doesn't have a dirty mind like the martial arts masters of anime. "Hey Greg! Good on you for not having that particular character flaw!" "RUB IT IN, WHY DON'T YOU?!"
Commentary added October 16, 2014