This works for me:

#!/usr/bin/perl -w
use strict;

chomp(my @banned_channels = <DATA>);

my $channels = "#gross_people #skriptk1dd13\$ #trolls";

sub IRC::print {
    print "@_\n";
}

foreach (@banned_channels) {
    if ($channels =~ /$_/i) {
        IRC::print "match: $_";
    }
}
__END__
#trolls
#flamers
#lusers
#litterbugs
[download]

However, I'd use a hash:

my $channels = "#gross_people #skriptk1dd13\$ #trolls";
my %banned;
@banned{split " ", $channels} = (1);

foreach (@banned_channels) {
    if (exists($banned{$_})) {
        IRC::print "match: $_";
    }
}
[download]