unfit for purpose

This expression originated with the Royal Navy where stores or equipment were found to be damaged, wouldn’t work or could not be used for the purpose for which they were intended. The expression quickly found wider usage and is now applied to not just stores and equipment, but to organisations, designs even concepts. It can also be applied to co-workers if they are not doing their job properly and, in extreme cases, used as a put down where someone is a complete arsehole and unsuitable to be considered part of the human race.