html.html

<select class="selectBox">
    <option value="disabled" selected="selected">Disabled</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
</select>
<select class="selectBox">
    <option value="disabled" selected="selected">Disabled</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
</select>
<select class="selectBox">
    <option value="disabled" selected="selected">Disabled</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
</select>
<select class="selectBox">
    <option value="disabled" selected="selected">Disabled</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
</select>

javascript.js

    $('.selectBox').change(function() {
        var current = $(this).val();
        $(this).siblings().each(function() {
            var val = $(this).val();
            if(current == val) {
                $(this).val('disabled');
            }
        });
    });