No trouser on the Tube day is here - or no pants Subway day if you're across the pond (but let's not get that mixed up).
Yes, anyone of a modest nature were in for a bit of a surprise, and perhaps averted their eyes on the Tube today.
Several hundred people braved the cold without their kecks for no simpler reason than, er, lols?
The display of bare flesh was originally a prank by New York's Improv Everywhere group in 2002 which has captured the imaginations of many around the world and is now in several cities and in its eighth year in London.
An open invite to exhibitionist Londoners to meet at 3pm in central London for the mission was accepted by many, before they headed to the Picadilly Line to take off their trousers.
Take a look at the pictures below (if you dare).