var getChecker = function(word){
   var r = new RegExp((
     '([' 
    + '\\\\' + word.split('').join('\\\\')
    + '])'
    + '.*?\\1'
   ), 'i');

   return {
     check : function(s){
       return !r.test(s);
     } 
   };
};

var test = function(units, fn, result){
  var i, len, unit;
  for(i=0, len=units.length; i<len; i++){
    unit = units[i];
    try{
      if( fn(unit) != result ){  
        console.error('not passed!');
        return;
      }
    }catch(e){
      console.error('not passed!');
      return;      
    }
  }
  console.log('passed');
};


var checker = getChecker('ABSNC');
test('AB BA AS SA ABS BAS SBA'.split(/\s+/), checker.check, true);
test('AA BB ABA BAA'.split(/\s+/), checker.check, false);

------解决方案--------------------
一个弄不来，用两个试试：
JScript code

var s='AB BA AS SA ABS BAS SBA AA BB ABA BAA'.split(/\s+/);
for(var i=s.length-1;i>=0;i--)alert((!/([ABSNC]).*\1/gi.test(s[i]) && /^[ABSNC][ABSNC]+$/i.test(s[i]))+' '+s[i])

------解决方案--------------------

 表达式：
!/[^ABSNC]|(.)(?=.*\1)/g.test(你要检测的字符串)

示例：
JScript code

<script>
var str = "AB BA AS SA ABS BAS SBA AA BB ABA BAA ABQ BWA ATS SAG";
var arr = str.split(" ");

for (var i=0; arr[i]; i++) {
    alert(arr[i] + "：" + !/[^ABSNC]|(.)(?=.*\1)/g.test(arr[i]));
}
</script>