RINO republicans don't look like rhinoceros. That the word makes no sense by itself means that you'd have to ask what they meant by it. If the acronym were "DUMB" or "CLOWN" or whatever then I don't think it'd stand out as much.

Also, you're right that it's often used in a way that wouldn't make sense grammatically if it were written out, but that's true for most acronyms I think; e.g. JPEG or GIF.

"Look at this funny Graphics Interchange Format I just sent you!"