The competitive undereating thread on here recently got me thinking: I haven't come across this 'penis portion' (men being served more than women) issue in my life, so I may be misunderstanding..
I can see it being sexist if the woman is being served a huge amount less, the man gets the nicest bits etc. But if it's more that both get a full serving but the man gets slightly more, maybe it's partly due to the host thinking (correctly) that the average woman might need slightly less?