"Good boy/girl" is a common phrase used to describe someone who has done something commendable. However, there are many synonyms available to use in place of this phrase. In the case of children, the terms "well-behaved," "polite," or "respectful" can be used. For pets, "obedient," "loyal," or "well-trained" can be great alternatives. In a general sense, one can use "excellent," "outstanding," or "exceptional" to describe someone who has performed well. Overall, there are numerous ways to praise and acknowledge someone's positive actions without resorting to the same old "good boy/girl" phrase.