onesie wednesday 2nd April coming

Now forgive me being a bit of a misery and cynic, but can someone please elucidate "onesie Wednesday" - maybe a NAS Moderator, as this is a NAS instigated fund raising event.

For one thing the idea that anyone wore attire like this was a revelation for me. Is this more American....or maybe a London thing.....?

But I wonder too what some spectrum folks think of rattling buckets in a crowded street wearing one piece pyjamas in a weird design.......