使用 off 解绑就可以。
target.off('focusin');
示例:http://jsfiddle.net/UUPHq/
<input id="test" placeholder="点我"/>
<span id="console"></span>
var target = $('#test');
var console = $('#console');
target.focusin(function() {
console.text('focusin');
});
target.focusout(function() {
console.text('focusout');
target.off('focusin');
});