Had she held her menu upside down, Harry wouldn't have batted an eyelash. He was far too used to Luna's quirks to be put off but such behaviour, public or not. He could even admit to trying to read one of his textbooks upside down ... just to see if he could figure out what Luna saw. Whatever it was, Harry wasn't gifted enough to see it.
"You're telling me," he chuckled, noticing how her nose scrunched up at the thought. "Most of the time I'd rather be writing a three foot essay for Snape." The both new that was saying a lot. Despite everything he'd learned about the man afterward, everyone knew that Harry was not a fan of potions. His thoughts briefly flashed an an irritatingly excellent potions master, but he shoved thoughts of that git back into whatever hole they'd crawled out of. He was suppose to be relaxing in Luna's company, not thinking of that git.
"I think it's the weather," he responded, folding his menu and setting it to the side.