Fruit or vegetable?

Yesterday we had an interesting lecture about the validity of 'truth-statements'.  The discussion was about which norm to follow.  Since we were speaking of pragmatists the notion of supra-material or metaphysical was out.  But even in normal affairs there was this dilemma of science or social?  The example that Huw Price quotes in his book Expressivism, Pragmatism and Representationalism (ch. 2) is that of tomato.  Now scientifically it is a fruit, but in ordinary usage it is used as a vegetable.  So the question, how do we treat it?  Go by science or by social usage?

What if someone sent me a gift: a basket of fruits ... tomatoes? Would I be wrong in feeling odd? Or is the person who sent me in the wrong?  What if I ask someone to get me some fruit to eat, and he gets me aubergines (English term for 'brinjal')? Would he be wrong? Would I be wrong in thinking he's gone nuts?

Or should we treat both, the scientific and the social understanding to be right? That'd mean that a tomato is both a fruit and a vegetable?