And the fact that the first time he doesn't do this she gets angry with him.
In Episode 14 Kanbaru answered her phone introducing herself as Araragi's love slave. She said this despite the fact that she apparently didn't know it was Araragi on the other end...in front of several children. Moments later she interprets Araragi's request for help to mean she should strip, which she then starts to do.
Prior to that the panic Kanbaru shows when Araragi points out that she isn't very perverted, prompting her to go after him.
In Episode 4 of Nisemonogatari Tsukihi walks in on Araragi in the bathtub... with Shinobunote who still looks like a childsitting next to him. Tsukihi returns moments later with a knife.
In Episode 5, Hanekawa gives Koyomi a "ticket" that allows him to touch her boobs as much as he wants, as long as he wants. Koyomi's pretty damn happy... until Hanekawa adds that she'd hate him forever if he used it. Koyomi immediately decides that it ain't worth it.