little bit o' language barrier

So I had just finished eating the pudding we got for winning in volleyball. It came in a nice glass that I was going to wash out and use at home.
Yamashiro sensei comes up to me at my desk:
Yamashiro: 'Sooooo.... cup... if you don't want... I can take it'
Me: 'Actually, I was going to save it.'
Yamashiro: 'Yes... but if you don't want....'
Me: 'No, I do want it.. I won't throw it away. I was going to wash it and I will use it at home.'
Yamashiro: 'Okay... but if you don't want, I can use when I make pudding.'
Me: ::finally realizing 'if you don't want' is the nice, subtle Japanese way of saying 'I want'::
'Ah, yes. No I don't want it... you can have it.' :)