Using us as insults

Once in a while I'll get into a heated discussion with a woman. Fairly often their go-to insult is that my dick is small despite the face that they they have no idea if it is. Over the last few years I've gained a lot of confidence talking to women. Not hating that I have a small dick. But one thing still bothers me.

When someone's default insult is "SMALL DICK" but it's somehow a good insult. It's unintelligent. Not clever. Far from original. But it's recognized as those things by people in general. A person who uses it is is revealing how dim-witted they are. But no one sees it. They just think "haha small dick"