From this to this
How did we get here?
Sagging is thought to be a manner of wearing trousers or jeans that sag so that the top of the trousers or jeans are significantly below the waist thereby revealing much of the underwear.
Sagging is predominantly a male fashion culture which originates in the 2000s.
Male fashionMen's fashionSaggingSaggy pantsYob culture
Very funny! I’m left gobsmacked every time I see one