yes, i think you definitely see if anything matches, and then negate that. So if it matches /evil|bad|wrong/ then it is a bad string that should be blacklisted. Now, that regex can be formed dynamically:

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;
[download]

Note that i took the liberty of using the /i modifier, and also added the word boundries. Also note that ?: is just so it doesn't needlessly capture.
Note also that look-aheads aren't needed here unless you care for some reason about the order of the blacklist hits, but it seems like you only care if they exist at all..

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