i have that issue man (under pressure)...i'll trade ya for it...
here's a tip...read "graffiti as an educator" on artcrimes this month. a very long, but VERY good read.
Think about it, you have writers learning the ins and outs of entire transport systems, risking serious injury even death, arrest and criminal records that would limit your opportunities for the rest of your life, for what? To simply paint a picture, does this seem logical to you? If the answer is no then it is most likely that you don’t fathom the idealism behind graffiti.