DO NOT use headphones! The objective of this day is for everyone within earshot to understand that it is the National Day of Slayer. National holidays in America aren't just about celebrating; they're about forcing it upon non-participants.
Taking that participation to a problematic level
Stage a "Slay-out." Don't go to work. Listen to Slayer.
Have a huge block party that clogs up a street in your neighborhood. Blast Slayer albums all evening. Get police cruisers and helicopters on the scene. Finish with a full-scale riot.
Spray paint Slayer logos on churches, synagogues, or cemeteries.
Play Slayer covers with your own band (since 99% of your riffs are stolen from Slayer anyway).
Kill the neighbor's dog and blame it on Slayer.
From CSTB and Paul Sommerstein.