A buck of a lifetime to me is one that you kill and you know you will never surpass the rest of your life. I don't think that it necessarily has to be the biggesst you ever take but something unique to that buck and hunt that can't be duplicated ever again.

I don't think you know what your buck of a lifetime really is until that special moment when it happens and everything comes together and the you know what a buck of a lifetime really is.