I see that Acadia informed us,

Put it this way...It was large and real, not cg...lol"

Are you saying that someone posted a picture of their erect penis?

And then after some message interchanges, deni67 asked a probing question,

Do you look at yours when it's at full mast and say, 
  "I must take a picture of that and put it online for others to admire as well".?

AFAIK, there is no reliable, specific rule that covers all possible instances and intentions ...

OTOH, it probably has a lot to do with the mathematical relationship between
the size of the ego and the size of what is to be displayed. 

In general, for most ego sizes, only the very largest endowments would be displayed. 

IOW,  if sizeof(endowment) > sizeof(ego) then display ...

In non-technical terms, that would be a result of being sure (confident) of offering
a unique display ... to the appropriate audience. 

OTOH, with smaller (lesser) egos, that determination is too easily reached
... i.e., a 'false positive'

In non-technical terms, since the smaller ego has less experience to draw upon,
that sort is prone to think there is more to display than reality would dictate. 

I will not provide visual confirmation in this forum
... could you just take my word on this? 

--
Martin
p.s. BTW, WRT automobiles, we often suspect an inverse relationship ...
Large car (or loud horn) appears important, but actually implies small ... you know what.