Well first, lets start with this model. Completely wrong look for someone who should be by some graffiti, this guy looks a lot more conservative rather than outgoing and unlawful haha. If you use graffiti get some gritty, tattooed friend or something, or a kid against authority, something that had more impact on the meaning that coincides with the graffiti.
In terms of the composution, where the guy stands and his gesture is okay, just isn't that interesting. Could have used a bit of a contrast boost(5-10 in LR) and a bump in saturation as well(I normally do about 10-20 depending on the photo).
As you said in your last post, you spoke of having some very shallow DOF. If you did this with a perspective that was very low(have him almost standing on top the camera), to make him seem larger than life it would have had a much better impact for the viewer.
Just my .02