I just asked someone how they were and they said, “I’ve had better days”.
Seeing as they’re British, this tells me they’re probably having the worst day of their life.
Seeing as I’m also British, I replied, “oh dear, sorry to hear that” and we left it there.
Etymology of the day is ‘bumf’: a shortening of ‘bumfodder’, 19th-century slang for toilet paper. It was later applied to any throwaway material or paperwork.