His posturing and playing along makes her respond in kind, shifting her weight slightly so the clothes she's wearing drape and hang in more appealing ways. It's subtle but direct: he may be the big strong one, but he's very... distractable.

"Prove you need them and I will," she answers in a soft purr. It's a direct invitation to show off for her, and a challenge. She doubts he'll be able to resist. If it pricks his ego a bit, she'll kiss it better later; no doubt he'll have plenty of chances to tease her in kind.