one of the things that sort of puts it over the top for me is the lettering. i know people who can fake griffin better than griffin, and they STILL could not have produced that lettering like that.
i dunno. he may have not known who the band was. he may have done it for some kid who simply asked. he may have been on one of his periodic benders and trying to be "opposite-man" who knows? griffin did an enormous amount of contradictory work in his time.
the idea that griffin actually did a slayer/punk poster is awesome. only "punky" street flyer type poster i've ever seen by griffin (if it is).