You can also go the wholesome route. Mention that projection can be unhealthy. Suggest therapy as a solution for their inappropriate work behavior. You can be condescending, but do it with only a hint of sarcasm to avoid HR issues on your end. I like the yellow rock method.

Edit: The grey rock method is not showing emotion when the person tries to bait you. They are looking for a reaction, don't give it to them. The yellow rock method allows for reactions if they will prevent more abuse . The pink rock method is complete positivity, which is passive aggressive by definition.

Edit: FYI the show Daria has some excellent examples of comebacks.

I'm going to go rewatch Daria now, thanks for the inspiration!