my $good = "this string contains no blacklisted tokens";
my $bad = "this string is evil and wrong";

my @blacklist = ('evil', 'bad', 'wrong');
my $re = join '|', @blacklist;

warn 'good string is ok' if $good !~ /\b(?:$re)\b/i;
warn 'bad string failed' if $bad =~ /\b(?:$re)\b/i;