Not to be that person, but you literally named yourself "lil_exhibitionist" and have a photo in a thread where men are trying to humiliate guys with smaller dicks.
The ones making a joke of the dicks around here are the "alpha bros" who associate large dick with being a "real man" and anything less than 8" just a shriveled up little clit, unable to please a woman.
In all my years of spending time on sex based forums (that's over a decade of time) I have only ever seen MEN make these comments. Men be complete dick sneezes to other guys, because they have an average dick and not some monster dick the others pump, stretch and fill with saline and silicone for.
There's also men who simply get off on their smaller size. They WANT people to say nasty things about their dick.
People as a whole are objectified for the sake of comedy. Small dicks, flat tits, big ass, fat people, dad bods, short women- (pocket sized pussy, amiright?), sex workers, women who are comfortable with their body and wear clothes others don't approve of, men who are more metro than masculine.
The list can go on. So, the question isn't about why it's acceptable to joke about small dick, the question is "why is it ok to objectify anyone for comedic or personal gain?"
I'm sorry if you've had negative experiences. People are strange, sometimes shallow and often times careless. Don't let judgey mcfuckfaces get to you.