I think it's not as much of a personal image we imagine unless someone asks us though.

It's more of just an exclamation that people use when describing a particular big buck that they, or more often someone else has killed...

"That's a buck of a lifetime!"

Which if you think about it, might simply mean that they don't believe they could do better... which I often take a smidgeon of offense to in my heart when I hear someone say it. Not that they have said it to me!