One of my girlfriends and I used to have a fun trick going on. At parties, she used to tell her girlfriends, in my presence, that I had a tiny dong. Then I acted embarassed, ashamed, a tad angry, etc... but faked it just enough so that some confusion persisted.
It wouldn't take long before her girlfriends understood that the opposite *might* be true and that it was all a joke. But the confusion was just big enough to keep them at bay.
My girlfriend liked the trick, because she always told me that she would *never* tell her girlfriends that I have a big one, because then she'd be afraid of the competition and of them perhaps trying to get it on with me.
A simple strategy that worked well for both of us. She had fun joking around about my size in ambiguous terms; I had fun because I never really had to reveal the truth, but could keep up the mystery. And all this in such a way that she didn't have to fear competition.
She told me repeatedly that she thinks no woman would ever reveal the truth about her lover/husband's size, out of fear of possible fights over the cock.
Of course, I will never know what she told her girlfriends when I wasn't present. In any case, our little trick - a genuine "insiders' joke" - was much fun and always got us excited.