There are several synonyms for the phrase 'speak evil of' which means to say bad things about someone. Some common synonyms include 'malign', 'defame', 'slander', 'vituperate', 'vilify', 'tarnish', 'disparage', 'smear', 'revile', and 'calumniate'. Each of these words conveys a slightly different nuance in meaning, but they all suggest speaking negatively about someone. It is important to remember that speaking ill of others can be hurtful and damaging, and it is always best to offer constructive criticism or refrain from commenting at all.