Toddler throwing things on purpose

I'd agree with Roshni on this! There can be many reasons why he's throwing things, sometimes it's just to seek your attention, sometimes it's solely because he is practicing motor skills. What you can do is to talk to him at his eye level (meaning squatting down to his level and maintaining eye contact) and tell him why he's not allowed to throw these things eg. because it's dangerous if they break and they're valuable items (try not to make expensive = valuable, but more of what it means to us like how his favourite toy is valuable) so we should cherish it. The next step you should do (after refusing it) would be to put those items away AND give him alternatives. Let him play with his toys, show him what he can throw (eg. soft toys, balls) so he doesn't feel limited or frustrated :) After which, just reinforce the idea and NOT make any huge reactions when he does throw what he's not supposed to.