that's a new one on me

that's a new one on me

That is something I was not aware about or did not know. A: "Yeah, Jeff and Anthony have been going out for a few months now." B: "That's a new one on me. I thought they were just friends." You aren't allowed to dump your grass clippings here? Well, that's a new one on me.
See also: new, on, one

a new one on (me, him, etc.)

an account, idea, or joke not previously encountered by me, him, etc. informal
See also: new, on, one

a ˌnew one on ˈme

a story, joke or piece of information that you have not heard before and which you may find difficult to believe: Butter that always stays soft — that’s a new one on me.No, I’ve never heard that story before. It’s a new one on me.
See also: new, on, one