[hunter2_]

I think what you're describing is a subset of sarcasm, or potentially a separate thing that often utilizes sarcasm (significant overlap). A friend of mine will often suffix such statements in speech with "if you know you know" in the event that the delivery alone isn't sufficient to trigger everyone's memory, and "IYKYK" in text.

Pure sarcasm has no such prerequisite, which means that delivery alone (tone, cadence, and smirk) is almost always sufficient. These give away the fact that sarcasm is happening to roughly the same extent that "/s" does, just that we have more experience with the former so the latter tends to feel too spoon-fed.