Come a cropper means to take a nasty tumble or crash and burn in embarrassing fashion. It originally referred to getting thrown off a horse, but these days it fits any plan that goes spectacularly wrong, from slipping on the pavement to blowing a work presentation. A handy phrase when someone’s confidence is loud and gravity is louder.
"Kev tried to vault the garden gate after the boozer and came a cropper into the wheelie bins, then swaggered off like it was planned."