Cum on boobs is showing your pride in these DD’s. In other words I will show you mine if you show me yours. Stroking your cock, while sitting in front of me. Telling me what it is that turns you on. Truly, I want to know. It is these big boobs, just big boobs in general perhaps.
Then again, it could be the areolas. The size, the shape, the small bumps. By all means come a little bit closer and inspect my boobs and see if it is indeed my areolas that make them ever so fascinating. With attention to detail, I think you should rub the tip of your cock over the small little bumps. Then over the nipples. See that is another thing that it could be. It could be the nipples.
In any event it could be both. Just having these large boobs wrapped around your cock could very well get you hard. Show me how much you love these massive tits. Give me your cum.