Happy (inter)national Day of Slayer

How to participate is posited succinctly at The National Day of Slayer HQ:

Slayer is a band from California. Their music has come to epitomize Satanic speed metal music in the latter half of the 20th century. Their 1986 album, "Reign in Blood" is one of the single most influential metal albums of all time, typified by the modern classic "Angel of Death".

Official Statement on Participation

Listen to Slayer at full blast in your car.
Listen to Slayer at full blast in your home.
Listen to Slayer at full blast at your place of employment.
Listen to Slayer at full blast in any public place you prefer.
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.