Is this grammatically correct? “I can’t unhear this” What does it mean?

Yes, the phrase "I can't unhear this" is grammatically correct. The expression means that after hearing something, one cannot erase or forget it from their mind. It often implies that the information or sound was surprising, shocking, or otherwise impactful, and now that it has been heard, it will linger in the person's thoughts. It's commonly used in informal conversations, especially when referring to something that was unexpected or difficult to process.