hey dude,
I think several guys here with art backgrounds provided different solutions.
Think of the overall objective/purpose of the drawing - for aesthetics sake, if your overall objective is to display an artist's view of himself - you, then address a few portions of the overall composition.
1. proportion - subject versus environment - think about the overall composition of your body in its environment - what do you want to emphasize in the picture? why?
2. your cock, like a male with big pecs or arms, or is just a part of the body, allow yourself to relax and find a comfortable position. the picture of your sitting on the ground is nice, but it emphasizes perspective, space, and shades. i am drawn the to negative space - floor and angles of your body (which makes it aesthetically pleasing.
3. think about the role of your cock in comparison to the body. is it to emphasize size and have the group react - if so, it's a bit pornographic - if not, and your are emphasizing the relationship of your cock, body, and environment to define a type of harmony, then it's art (weird, right).
4. Think about the mediums you plan to use - charcoal and pencil - great - wet mediums a bit difficult, but doable.
5. how do you want to connect to the viewer? how should they feel? what does tale does this picture tell? is it a defining picture defining your role as an artist or are you beginning a new chapter in your artistic expression?
These are all things we think about as artists (former MICA student and architect here).
Have fun and i would love to know what you discovered about yourself and cock in relations to your body and environment.