They think it annoys you. They do it to wind you up. That is the concise and precise answer.
One of the great spectacles of the gun control debate is watching progressives:
Resort to crude stereotypes (generally absurd ones based on, apparently, Deliverance or country music or something.)
Classism (which is okay when it's the poor whites who own guns who they assert are toothless ignorant yokels). Just never say shit about any other demographic than poor whites or it's some form of *ism.
Body-shaming (penis). Try accusing a feminist of only hating men because she's flat chested though, and watch what happens.
Government lists (a scarlet letter when you do it to communists or people on the Soviet payroll or whatever, but, totally cool when it comes to gun owners).
Prohibitionist logic (drug war bad, people get drugs anyway/grows prison system. Abortion bad, people have back alley abortions. Gun control though will totally work and reduce gun violence because how can someone possibly get their hands on a gun if there's a law, paperwork, and bureaucracy prohibiting it because gangs will totally get discouraged over the paperwork and just become social workers instead.)
And pushing policies which basically disarm citizens, leaving the very cops they claim to fear (or hate) with a monopoly on firearms. This is the most interesting thing of all, for those who are actually pushing prohibition (no one is coming to take your guns of course, except for all of those who are).
Gun control brings out the most ludicrous sort of hypocrisy on the soft Left (left-anarchists and the like understand the need for civilians to own firearms but don't apparently feel the need to break a nail getting involved in this fight - attacking from the Left as they should be - as they're positive some anarchist coffee shops and the occasional WTO riot will bring the whole system down without the need of arms. Also some bourgeois white conservative might benefit and they can't have that.)
If it is true that the most homophobic people are the ones who are closeted gays themselves (I hear progressives claim this all the time), I seriously wonder what that portends for people who can't have a discussion or debate without dragging penis into it.
What is interesting about the penis thing isn't that progressives have to drag cock into the discussion (progressives in recent years are obsessed with cock; you'd think transgender people were like half our population), but that even if it could be shown that gun owners have universally small dicks, how they're suddenly comfortable using body shaming as a form of mockery when they go absolutely apeshit when someone does it to a woman over some other issue.
Despite being pro-choice, a believer in global warming and distressed at the current state of our ecosystem, and despite being for gay marriage, drug legalization, and a bunch of other progressive things, it is the ugly hypocrisy of the anti-gun progressive who claims to speak truth to power and call out all that oppresses us, while disarming the very classes whose interests they claim to represent, which lets me know I'm not a progressive at all.
As ugly as they think the modern gun owner is, being progressives, we can count on them never to look at themselves, or accept any blame for the fruitlessness of this discussion. Their complete lack of self-consciousness as they willingly become all they despise when they talk about this issue broadcasts the moral bankruptcy of the Left in general -- those people on the Left who see these same things excepted, of course.
Small penis, large penis, the answer is still, "No."