http://www.perlmonks.org?node_id=438205

Just finished this one:
perl -le 'my $c=$^X . " -le \" sub a{(\\\$a)=\@_;\\\$a=~tr/A-Za-z/N-ZA-Mn-za-m/;\\\$a;} my \@f=\(\\\"unpxre\\\",\\\"whfg\\\",\\\"nabgure\\\",\\\"crey\\\"\);\160\162\151\156\164  ucfirst(a(\\\$f[1]).\\\" \\\".a(\\\$f[2]).\\\" \\\".a(\\\$f[3]).\\\" \\\".a(\\\$f[0]));\"";do{eval(exec($c))};'

***Update***

I could not resist to make it more unreadable :-)
perl -le 'my $c=$^X . " -le \" s\165b \141{\50\\\$a\51=\@_;\\\$a=~tr/\101-\132\141-z/N-ZA-Mn-z\141-m/;\\\$\141;} my \@f=\(\\\"\165n\160xre,\\\",\\\"w\150\146g\\\",\\\"n\141\142g\165re\\\",\\\"\103\162\145y\\\");\160\162\151\156\164  ucfirst\50a\50\\\$f[1])\56\\\" \\\"\56a\50\\\$f[2])\56\\\" \\\"\56\141(\\\$f[3],,,,,,,,,,,,,,,,,,,,,,,)\56\\\" \\\"\56\141(\\\$f[0],),,,),,,;\"";do{eval(exec($c))};'