Well, assuming you have fixed length data so that you know YES occurs at index 25 in the string given, I'll use my PSI::ESP module and guess that you've read in lines of data into an array (@arr), and that the YES string is supposed to occur at the end of that line and you haven't chomped the newline off the end of the line -- thus you are trying to compare "YES\n" eq "YES". If this guess sounds right, try doing a chomp $contact_me; prior to your inner conditional test as in:

#!/usr/bin/perl -w
use strict;
my @arr = <DATA>;
my $contact_me_count = 0;
for my $lcv (0 .. $#arr){
    if($arr[$lcv] =~ /^CONTACT_ME:/){
        my $contact_me = substr("$arr[$lcv]", 25);
        chomp $contact_me;
        if($contact_me eq 'YES'){
            $contact_me_count ++;
        }
    }
}
print $contact_me_count;
__DATA__
CONTACT_ME:              YES
CONTACT_ME:              NO
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