落ちんなよ。(a colloquial form of 落ちるなよ mostly used by males)
Careful! (lit. Don't fall down!)
That's a warning to Eita(the guy who is going to pick the orange from the tree).
FYI, we can't see the video in Japan due to "This video is not available in your country" error. I watched the drama in another site, so I can't judge the validity of the given English translation.