There isn’t one. People have probably been told (or even warned) to knock it off with that stuff because Dopers are experts at running jokes into the ground, and some of the buckeye stuff became borderline (or not so borderline) harassment of OpalCat. I wouldn’t be surprised if someone was told “Enough with ‘Hi Opal’ already” at some point, but there’s no blanket rule against either. People frequently misunderstand instructions like these.
No, I just didn’t read that one carefully enough.