In the elevator.
When Johanna had stripped herself of that awful tree costume it certainly hadn't been for Peeta's benefit. And if Katniss's annoyed glare was anything to go on she certainly thought that it was. But oh no, Girl On Fire. Contrary to popular belief, Johanna Mason doesn't strip for just anyone. And that's all Peeta was to her. Just anyone. But Katniss intrigued her, and she wanted to know if she intrigued Katniss too.
The younger victor's expression was kind of priceless actually. But wait, did Johanna see something else behind all the annoyance? It was hard to tell as she chatted with the boy about his paintings, pretending not to seem too interested in Katniss or what she was doing. But interested she was, and no matter how much the younger girl wanted to pretend she wasn't just as interested, Johanna just happened to glance over in time to see Katniss's eyes flicker down to her bare breasts. She looked back at Peeta to see his eyes in the same place. Poor boy, by the looks his 'fiancée' was giving her, she'd guess this was the first time he'd ever seen boobs.
She flashed a smirk at Katniss who was now openly staring. The younger girl quickly averted her gaze and Johanna could just make out a faint blush under all the makeup. This girl was just too easy.
The elevator stopped on the seventh floor and Johanna winked at Katniss before turning to exit. She could practically feel their eyes on her ass and she swayed her hips a bit for show.
"Thanks. Let's do it again sometime."