deafamation
Derogatory/critical remarks/claims made in the presence of the person whom you're throwing under the bus, with the assumption that said criticized individual will not know what you're saying due to hearing-impairment.
A good example of deafamation's "coming back to bite you" is the classic humorous tale of the old fella who got a hearing-aid without his family's knowledge, and then he was able to repeatedly change his will while surreptitiously listening to the conversations of said family-members, since he now knew what they really thought of him and what their future plans were to spend whatever assets he'd originally been planning to leave to them.