Reporting the bug here since it looks like upstream is mostly-dead.
This is what happens when xclip-copyfile is ran with the --help flag:
$ /usr/bin/xclip-copyfile --help
tar: Usage\: dirname NAME\n or\: dirname OPTION\nOutput NAME with its last non-slash component and trailing slashes removed;\nif NAME contains no /'s, output `.' (meaning the current directory).\n\n --help display this help and exit\n --version output version information and exit\n\nExamples\:\n dirname /usr/bin/ Output "/usr".\n dirname stdio.h Output ".".\n\nReport dirname bugs to firstname.lastname@example.org\nGNU coreutils home page\: <http\://www.gnu.org/software/coreutils/>\nGeneral help using GNU software\: <http\://www.gnu.org/gethelp/>\nFor complete documentation, run\: info coreutils 'dirname invocation': Cannot chdir: No such file or directory
tar: Error is not recoverable: exiting now
The same thing applies to xclip-cutfile and xclip-pastefile.
While this isn't _technically_ a bug (as the parameters are simply passed to tar), most users would probably expect to see the applications usage, rather than being bombarded with that jarring text.
Also in https://github.com/astrand/xclip/issues/16
As already discussed here and in the upstream issue this is not really a bug and unless a fix for this is accepted upstream I do not think it would be wise to potentially change compatible behavior in Gentoo only. I made a comment on the upstream issue to see if they are interested at all.