<?php
 
$str = "men's black hat, white shirt and orange shirt!";
 
$words = preg_split('/\W*(\s+|$)\W*/', $str, -1, PREG_SPLIT_OFFSET_CAPTURE | PREG_SPLIT_NO_EMPTY);
 
$targets = array('hat', 'shirt');
$shield = 'men\'s';
$bias = 0;
 
for ($i = 0; $i < count($words); ++$i) {
    list ($word, $offset) = $words[$i];
 
    if (!in_array($word, $targets)) {
        continue;
    }
 
    for ($j = max($i - 2, 0); $j < $i; ++$j) {
        if ($words[$j][0] === $shield) {
            continue 2;
        }
    }
 
    $replacement = 'FOO';
    $str = substr_replace($str, $replacement, $offset + $bias, strlen($word));
    $bias += strlen($replacement) - strlen($word);
}
 
echo $str;

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