完美的解决方法想不出来，毕竟还是渣渣。
想到一个比较丑的方法，看看就行：

$str = "1111111111111112b22222222caonima22222222";
$words = ['2b','caonima'];
$res = [];
foreach($words as $word){
    $res[$word] = count(explode($word, $str))-1;
}
return $res;

如果说是只统计脏话次数，并不要求每一个脏话的次数，之前写过一个根据多个key切割字符串的函数

$str = "1111111111111112b22222222caonima22222222";
$words = ['2b','caonima'];
function many_explode($cutKey,$string){
    $return=[];
    $key=0;
    for($i=0;$i<strlen($string);$i++){
        if(in_array($string[$i], $cutKey)){
            $key++; //当前字符在 cutKey 中，跳过，并另起一行
        }else{
            $return[$key]=isset($return[$key])?$return[$key].$string[$i]:$string[$i];
        }
    }
    return $return;
}
return count(many_explode($words, $str)) -1;

换汤不换药

1,所有的脏话的关键词建立一个表.
2,内容context 做全文索引.
3,使用mysql自带的函数检索locate,或者你用like也可以.

$arr = array('2b', 'fuck');
$con = array(
        array(
            'content'=>'asdfasdf2bsdfasdf2dfasdfuck'
            ),
        array(
            'content'=>'asdfasdf2asdfasdf2dfasdfuck'
            ),
        array(
            'content'=>'asdfasdfuckbsdfasdf2dfasdfuck'
            ),
    );

foreach($con as $ck => $cv) {
    foreach ($arr as $av) {
        if (($pos = strpos($cv['content'], $av)) !== false) {
            $cv['checkCount'][$av] = recursionSearch($cv['content'], $av, $pos, 1);
        }
    }
    $con[$ck] = $cv;
}

print_r($con); //
function recursionSearch($haystack, $needle, $offset=0, $res=0 ) {
    $offset += strlen($needle); 
    if (($pos = strpos($haystack, $needle, $offset)) === false) {
        return $res;
    } else {
        return recursionSearch($haystack, $needle, $pos, $res+1 );
    }
}

// 打印结果
/**
Array
(
    [0] => Array
        (
            [content] => asdfasdf2bsdfasdf2dfasdfuck
            [checkCount] => Array
                (
                    [2b] => 1
                    [fuck] => 1
                )

        )

    [1] => Array
        (
            [content] => asdfasdf2asdfasdf2dfasdfuck
            [checkCount] => Array
                (
                    [fuck] => 1
                )

        )

    [2] => Array
        (
            [content] => asdfasdfuckbsdfasdf2dfasdfuck
            [checkCount] => Array
                (
                    [fuck] => 2
                )

        )

)
**/

谢谢回答合各位的回答，学习了多种写法。 用了qvga提供的第一种，后面加上array_sum统计了总数。 在次谢谢^_^