Rose not actually hating him was something of news to Frank. A little, at least. Hate was a strong word, that much was true, but he definitely didn't think that she liked him. That, too, seemed like a word that didn't fit them. He felt quite such that she was trying a little too hard to confuse him on the matter of her opinion, and it was certainly working if his bemused expression was any indication.
However. It did occur to him that it would likely make Rose highly uncomfortable if he acted like he did not, in fact, know better. So obviously he had to use it against her, at least a little.
"Shh," he hushed her sharply, looking around dramatically. "You really don't want people to overhear that you like me, Rose? Perhaps you shouldn't go broadcasting it like this."
Of course, the Malfoy thing was entirely valid, and he spared her whatever blustering attempts at covering herself that he knew were coming -- or tried to, anyway, by instead saying even more nice things about himself. Because that, surely, would help rather than making matters worse. "Well, Peeves is quite a fan of mine, so of course he was willing to do as I asked in favor of irking Malfoy for as long as he can stand it. Though, I don't wager it will very for all that long, actually."