I can only speak for myself, but it is important to me not to be objectified or only seen as the guy with the big dick. I am a well rounded, well educated and sociable person who has a dick that happens to be larger than some guys and smaller than others.
At the urinal or in the locker room, a glance and a nod are appreciated. It's nice to be acknowledged. It's not so nice to be grabbed or called out loudly unless that's already a part of your relationship.