I think it's humorously rude. If someone said it to me seriously, along with the palm of the hand shown to me, I would be rather offended. However, I hear it quite a lot and not only from the younger generation (surprisingly) and it's usually said with a wry smile.
It basically means "I'm not interested in listening to you so feel free to keep talking but you'll just be talking to my hand".
I tend to associate it with people appearing on, for example, the Jeremy Kyle show. I think I first heard it on an American version of that sort of show, possibly Jerry Springer.
Talk to the hand (GQ India magazine)
"But even as Modi’s lawyers argued that the BCCI wouldn’t hand him a clean chit, the judges weren’t playing ball. In fact, at one point, one of them is believed to have put up his right hand and muttered “Talk to the hand”, but confirmation on that is still pending"
It is hard to imagine a judge doing this, if it is true. The BCCI is the Board of Cricket Control for India, a body headed by controversial people, some of them politicians.
Here is another instance -
Talk to the Hand (and other ways of talking to Indian MPs)
It appears to me that the writer is saying that Indian MPs are asking people to 'talk to the hand', and not even providing an email address, for example.
But I don't know what this advertisement means:
Talk to the hand
They're just using the phrase as a convenient title- this watch will talk to the owner's hand in a positive way by looking good.