The act of fooling around and not doing your job. More specifically, the act of writing, or spraying, the numbers 40 on a
wall in an undeniable reference to a 40
rock of cocaine. It's mostly used as an excuse for not doing your
work.
Person 1 "Are you slacking off again?"
Person 2 "Nah man, I'm
testing spray patterns!"
OR
Person 1 "Why are you writing 40 everywhere?"
Person 2 "I was just testing
spray patterns."