To be understood, I’d probably just say projection. If you need to emphasize a specific aspect of the behavior, you could break it down as a maladaptive inferiority complex that prompts social anxiety evidenced by momentary paranoid ideation and compulsory preemptive introjection.

Explanation: introjection refers to a mirroring behavior common in children. In this case, the accuser anticipates an accusation from you. To defend themselves, they hurl the accusation right back at you. But of course the first accusation only happened in their head, so all we witness is someone wildly accusing someone else of having their own flaw.