Speaking ill of someone is a demeaning act that can harm or hurt someone's reputation. To avoid making someone feel bad, it is always better to use neutral language or communicate your feelings in a constructive and respectful way. Some synonyms for the phrase "speak ill of" include badmouth, disparage, slander, malign, defame, criticize, smear, belittle, insult, and vilify. These words all imply a fault-finding attitude and can have a negative impact on the person being spoken about. It is important to always remember to choose our words carefully and treat others the way we want to be treated.