blot, smear, smirch, spot, stain -- (an act that brings discredit to the person who does it; "he made a huge blot on his copybook")
Overview of verb smirch
The verb smirch has 2 senses
smirch, besmirch -- (smear so as to make dirty or stained)
defame, slander, smirch, asperse, denigrate, calumniate, smear, sully, besmirch -- (charge falsely or with malicious intent; attack the good name and reputation of someone; "The journalists have defamed me!" "The article in the paper sullied my reputation")