When I saw or knew something, but currently I don't remember it, and after someone talks about it it revives my memory, what expression(s) may I use?
For some reason, probably heard someone saying but it's wrong, I got used to say: "sorry, it wasn't on top of my head".
I asked a native English speaker and he had trouble finding expressions for it.
I don't want something cold like "sorry, I couldn't remember". Something funnier, friendlier.
Is there an English expression for that? Any idea how I ended up with "on top of my head"? I actually like it, but I understand it is wrong.