British Word of the Day

Yoix!

Come a cropper:
'Then along comes this Melville with his man-about-town manners and sweeps her off her feet.  But it won't last; she's going to come a cropper, poor girl, but she'll be none the worse.'--Off With the Old Love

I found this short article on The Phrase Finder about the meaning and origins:

For the actual derivation we need to consider the nether quarters of a horse - the croup or crupper. In the 18th century, anyone who took a headlong fall from a horse was said to have fallen 'neck and crop'. For example, this extract from the English poet Edward Nairne's Poems, 1791:

A man on horseback, drunk with gin and flip,
Bawling out - Yoix - and cracking of his whip,
...
The startish beast took fright, and flop
The mad-brain'd rider tumbled, neck and crop!

'Neck and crop' and  'head over heels' probably both derive from the 16th century term 'neck and heels', which had the same meaning. 'Come a cropper' is just a colloquial way of describing a 'neck and crop' fall. The phrase is first cited in Robert S. Surtees' Ask Mamma, 1858:

[He] "rode at an impracticable fence, and got a cropper for his pains."

By the time John C. Hotten published his A Dictionary of Modern Slang, Cant, and Vulgar Words in 1859, the phrase has come to refer to any failure rather than just the specific failure to stay on a horse:

"Cropper, 'to go a cropper', or 'to come a cropper', i.e., to fail badly."

Maybe an equivalent vulgarism might be that 'he landed on his [bleep]'.  Come a cropper is more suitable to all occasions.  Let's start a movement.