I definitely object to some of the comments here. Children are children and as such, are still learning and it is up to all of us to model behaviour.
Do not take it at face value. Sometimes children behave in this way because they are unsure. Maybe the child had never tried a jigsaw before and hence did not want to lose face. Very few children of that age actively dislike dinosaurs. In this situation, with any child, my own GD/Ss included, I would engage with the child. Picking up the present I might say. ‘What a shame, we love jigsaws don’t we X? Do you like dinosaurs? This jigsaw looks really hard – it’s got x number of pieces. I think I would need help with that. Shall we all give it a go?’ Twist the conversation round to your own ends or try a different tact. You are the adult! Once you have established a rapport, address the behaviour. ‘X chose that especially for you. Do you think it was kind to say you were going to throw it in the bin? I would hate it if someone did that to me! Do you think it would be a good idea to say sorry?’ The majority of children would act positively to this approach.
I am probably teaching many gransnetters to suck eggs but I will never condemn and give a ‘wide berth’ to a four year old!