Sentence:  A little girl in pink exited one of the stalls with her mother behind her. “I wear big girl underpants now!” she proclaimed. She looked up at my sister. “Do you wear big girl underpants?” Nicki stared down at her. “No, I generally <WSD>go commando</WSD>.” 
Meaning of the word marked with <WSD> tags:  To forgo wearing underpants under clothing.