Peter,
I realize the point of your thread is not to debate nominations for the worst hole in the world, but as I am very familiar with Ballybunion New and a close friend assisted Robert Trent Jones on the placement of the green I think you are refering to, let me just mention a few things:
First, I assume you are refering to the fifth hole. No other hole comes to mind that fits your description.
I won't argue that it is a great hole, but actually, when the area behind the green is properly maintained, it can be kind of fun. By property maintained, I mean the grass is cut sufficiently so that if you land anywhere near the green usually the ball will come back to the green.
I've sat for hours watching people play the hole and played it many, many times. Usually, with any kind of decent approach shot, you are left with a putt, thanks to the back board effect of the hill when properly maintained.
Funny things is that Mr. Jones actually designed two greens on that hole, with one to the left and far higher up the hill.
That might have been the worst hole in the world and it was abandoned in the early 90's.