Is there actually a "butterfly that looks like a bird's face" and, if so, what is its name? I don't know, that's why I'm asking. I can't very well comment on it unless I see what it is.
Otherwise, to the best of my knowledge, the giraffe's neck is typically thought to be long for browsing, not for masculine display, and so I don't see where the dispute might be. In other words, so far as I know, evolutionists more so than not agree with you that the elongated neck is for browsing, and therefore that giraffes fight with their necks simply because that's all they've got given their anatomy.
So, my first reaction to whoever said that long giraffe necks evolved to display dominance might have a viable hypothesis, but not an obvious one. It seems like there are a number of simpler explanations.
And, the best way to test it, off the top of my head, would be to simply investigate whether longer-necked male giraffes are more likely to reproduce.
A fair number of butterflies and moths have hindwing markings that resemble eyes.
It is thought that they may fool birds into thinking the butterfly is not appropriate prey.