blot (one's) copy book

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blot (one's) copy book

To tarnish, damage, or ruin one's reputation by behaving badly or committing some mistake or social transgression. Refers to a child's copy book, the blotting (staining with ink) of which ruins one's work. Primarily heard in UK. The local councilor blotted his copy book when it came to light that he had accepted bribes to allow unregulated development projects to go ahead. I really blotted my copy book when I spilled my drink on the visiting dignitary last night.
See also: blot, book, copy

blot your copybook

BRITISH
If you blot your copybook, you damage your reputation by doing something wrong. Their relationship had been so perfect. Until he'd blotted his copybook with Susan, that is. Note: You can also say that there is a blot on your copybook. In fact, just about the only blot on his copybook so far was a missed penalty against Arsenal 10 days ago. Note: In the past, schoolchildren had `copybooks'. These were books of examples of handwriting, with spaces for the children to copy it.
See also: blot, copybook

blot your copybook

tarnish your good reputation. British
A copybook was an exercise book with examples of handwriting for children to copy as they practised their own writing.
See also: blot, copybook

blot your ˈcopybook

(old-fashioned, informal) spoil a previously good record: He paid back the money he had stolen, but he had blotted his copybook and couldn’t hope for promotion.A copybook was an exercise book with printed examples of good writing for children to copy. If you blotted it, you accidentally spoiled it by making a mark with ink on it.
See also: blot, copybook
References in periodicals archive ?
Tommy Smith scored for Derby on 17 minutes but Lee McCulloch equalised moments later - only to blot his copy book with a late red card.
Young did blot his copy book slightly by being sin-binned for punching, along with Edinburgh's Martin Leslie midway through the second-half.
Massey had taken the lead through Dave Inniss only for the scorer to blot his copy book as his wayward back pass let in Micky Martin for the equaliser and Sphinx added second half goals through Jamie Towers (2) and Paul Gibbons.
Roberts did blot his copy book when he showed excellent skills in the box after 83 minutes and then dropped to his knees looking for another penalty and was booked.