blot
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.
a blot on the escutcheon something that tarnishes your reputation.
☞ An escutcheon was a family's heraldic shield, and so also a record and symbol of its honour.
a blot on the landscape something ugly that spoils the appearance of a place; an eyesore.
1962Listener Charabancs and monstrous hordes of hikers are blots upon the landscape.