To Pass the Boof simply means to hand someone a marijuana cigarette that you are smoking.
In this case, “boof” is just another word for “joint”, “blunt”, “spliff”, or numerous other names used for cannabis cigarettes.
You would say Pass the Boof to your friend who has been holding on to your shared weed cigarette for a bit too long.
Boof, as a synonym for weed, originates from Washington DC, US. It was first described by user iamSWISH on Urban Dictionary in 2014.
The slang Pass the Boof was then made known by rapper Keychainz Hefner in June, 2018, in his rap song with the same title.
Pass the Boof was later edited into already existing meme formats, often with a blunt, or boof, edited into the image as well. The first such meme was posted on Reddit 10 days after the rap song was released.
The Reddit post was immediately shared on multiple social media platforms, consequently inspiring the creation of other versions.
Elon Musk smoking weed was already an existing meme format, but was recreated with the text Pass the Boof, gaining increased popularity to the slang.
The Elon Musk format plus the Avengers format featuring Thanos passing a boof are the most shared versions of the meme.