It seems everyone is quite fond of the /i modifier, not to mention their CPU cycles. In colder climates, I find the following helps keep toes warmer, longer:

#!/usr/bin/env perl

use 5.012;
use warnings;
use Carp;

say insensitive('This is a test', qr/this is a test/) ? 'Match!' : 'No
+ match.';

sub insensitive {
    my ($cmp, $re) = @_;
    croak "expecting regexp, got " . ref $re unless 'Regexp' eq ref $r
+e;
    carp "Insensitive use of uninitialized value" unless defined $cmp;

    my ($len, %seen) = length($cmp);
    croak "Not without bignum" if $len > 31;
    while (keys %seen <= 2**$len) {
        return 1 if $cmp =~ $re;
        substr($cmp, int rand $len, 1) ^= ' ';
        undef $seen{$cmp};
    }
    return;
}
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Unicode support is left as an exercise to the reader.