If you know the items are always sorted, there's a routine that's likely to be faster than anything else shown here as I post this:

my $ok = no_common_item_in_these_numeric_sorted_lists(
  [1, 2, 3],
  [2, 4, 6]
);

sub no_common_item_in_these_numeric_sorted_lists {
  my @x = @{+shift}; # these are copies
  my @y = @{+shift};
  ## presuming numeric sorted
  while (@x or @y) {
    shift @x, next if not @y or $x[0] < $y[0];
    shift @y, next if not @x or $x[0] > $y[0];
    return 0; # not ok - we found an identical item
  }
  return 1; # ok - we found no identical items
}
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-- Randal L. Schwartz, Perl hacker
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