4/20 Day

Golden Gate Park, San Francisco, 20 April 2010: an XXL marijuana joint is lit to celebrate '4/20' day ('four-twenty day'; also, 'weed day' or 'pot day') the annual convention of pot fans and advocates for the legalisation of marijuana, held (obviously) on the 20th of April. Apparently, the name comes from the time at which back in 1971 a bunch of friends would meet regularly after school (San Rafael High School California), to have a joint.

Image source: METRO