Red Pants Monday is a weekly event in the BBC Sherlock fandom, primarily on tumblr among shippers of Johnlock, featuring art and/or fanfiction of John Watson in a pair of red y-fronts.

John is often accompanied by Sherlock in a pair of black and white y-fronts with bees. Of course, the underwear don't tend to stay on for long.

This trend was started by the lovely tumblr user and artist, reapersun, and though the event is not as popular as it was before it still has a following.