I remember seeing Batman Forever as a child in theaters and thinking it really kicked ass (being maybe 13 I was blissfully ignorant ) because of the snappy Chris O' Donnel "Holy rusted metal Batman!!! I mean look...all around us...holy rusty metal..." but now I realize it was just Schumacher making an impotent, fleeting homage as he dragged the shuddering, slashed to ribbons, all but lifeless body of Batman towards the wood chipper.
This clip is like a shot of Johnny Walker Black, and here is the perfect chaser http://tinyurl.com/6k9363
So were the writers just having a contest to see who could come up with the most ridiculous expresion?
Or is "holy" simply a replacement word for "fucking"?
The expression "Holy Cow!" is the original, and it's pretty much a replacement for "Jesus Christ!" in that you're blaspheming against a god that isn't your own, while having a fun poke at the funny people who worship cows. Fun fact- "Judas Priest" is also a friendlier way of taking Jesus' name in vain.
Really, when you put all these together, it sounds less like a catch phrase and more like Robin has a debilitating verbal crutch.