Blot (one's) copy book British Verb + object/complement informal
To do something that spoils one's reputation
The star football player blotted his copy book by throwing a water bottle at the referee.
I really blotted my copybook by being late for this morning's meeting.
That teen singer really blotted my copy book when she was seen drinking to silly many times.
1. To shame someone/something.
2. To achieve better results than someone/something.
To be in disfavor or disgrace.
The verb "blot" should be conjugated according to its tense.
The expression derives from children making blots or ink spots on their school copybooks (writing books) and thereby spoiling them, which they used to do, literally, from at least the early 19th century.