What if you write for comic books
? And what do you do if your medium is "WARNING!
I am a writer by trade, and I have to say I generally find rules of thumb unhelpful. Sure, the exclamation point is something that is perhaps best used sparingly, but if your writing calls for one then, hell, stick one right in there! Damn the consequences!!
(PS: I have only two thumbs, with which I will now spell "nvnvnvnvnvnvn.")