my @list_of_stuff = get_my_list();
foreach my $i (0 .. $#list_of_stuff)
{
    foreach my $j (0 .. $#list_of_stuff)
    {
        next if $i == $j;

        do_compare($list_of_stuff[$i], $list_of_stuff[$j]);
    }
}

##</code><code>##

Things Comparisons
  2         1
  3         6
  4        12
  5        20
 10        90
 15       210
 20       380
 25       600
 50      2450
 75      5550
100      9900