covert hostility

Covert hostility is antagonism disguised behind a veneer of politeness or neutrality.

Unlike open aggression, it operates through subtle means—backhanded compliments, deliberate omissions, or feigned helpfulness that somehow never helps: Her covert hostility showed in how she'd "forget" to include him in important emails.

The phrase appears frequently in psychology and workplace contexts to describe behavior that's difficult to confront precisely because it maintains plausible deniability.