Trying to install Homebrew, but I get this "fatal: cannot create directory at 'Library/ENV/pkgconfig/10.10': Permission denied"
I would suggest go and visit 'Library/ENV/pkgconfig/10.10', if it's there, try to look at its permission, if it differs, try to delete it and re-run the installation.

It happen to me once also but it's coming from sass/grunt. Permission denied just to find out that special file was created by other user (because I copied it from somewhere) and it have overriding problems, thats why it return permission denied.

Well, that's my case, hope this little stuff might help you. Who knows :P