The OED reference to the phrase right as rain to being now chiefly Australian and New Zealand colloquial would explain why my relatives in those countries use the phrase so liberally.
Harumph!I think the OED may be nursing a grudge against the former "colonies" especially us rabble rousers here in New England!
"Right as rain" is often heard here. I don't know about teenagers but heard it from a 30-something not long ago.
Mumble mumble mumble
wow