Sorry man, despite the convenience, I don't think we were given a penis to be used as a towel hook. That exclusively male organ is capable of delivering too much pleasure than to be wasted as a space for an unused towel. Not only that, but just think about how ridiculous it looks with a limp towel hanging from it. None of us can sustain an erection permanently!
I know this much: whenever I get an erection, it is too distracting and uncomfortable for me to walk around with one raging permanently! Ouch! No, thank you! Do not hang your towel on your penis!
Another observation: towels are way too flimsy to be used as a modest wrap. They flap around and rarely tie securely. If damp, they refuse to stay tied and often come undone. If you try to sit while wearing one, the penis generally flops out. Forget using it for the sake of being modest. Just go naked!
If you absolutely must have a towel with you when nude outdoors, follow the example of the guy below and wear it around your neck! One of the many reasons that we're clothes-free is to see and to be seen!
Otherwise, just carry it with you but always in the open position! Nothing beats being nude and strutting your stuff!
Be yourself: gay, nude and proud!
Rashad