I don't know if he's serious, but he's wrong. Don't do anything illegal. Try to unsubscribe first. If you have the capacities, and you suspect it's a smaller corp or mailing list, get a huge (50MB+) picture featuring a huge "unsubscribe" text. Call it "IDontwantyourjunkpleasestopspammingme.jpg" and send it. Most of them understand what you are saying if you do it once or twice. You'll need the capacity for it, but then, if you have a flatrate at home, and dont need your comp when you are sleeping and at work/school, you have about 16 hours of free capacities... and it's completely legal to trash their inbox, after all, they do it every day. ( ever got a 1.5 GB attachment *g* I never got any mail from them after that... ). You might want to seperate it in smaller junks because your own mailprovider might not be fond of one large attachment *g*
Filtering might be the easiest way though.
I think in europe we have good chances to make spamming illegal... they approved the first laws leading in the right direction.