a new one (on me)

Something I was not aware or informed of or knew nothing about until just now. A: "Yeah, Jeff and Anthony have been going out for a few months now." B: "That's a new one—I thought they were just friends." Having to pay for the water you use in your house is a new one on me—is that an American thing or something? I need a quarter to get a shopping cart from the rack? Well, 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.

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.