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It is stealing if you click your adsense ads.
It is stealing if your friends clicks your adsense ads for you.
The usual response to this is "Well, I'll only click on ads that I am interested in. And I'll tell my friends to do the same" So let me cover that now: Who are you kidding? You don't visit a site that you profit from to look at ads. Neither do your friends.
That covers WHY you shouldn't do it, But your question seems to be what happens. In short: You will make about $10-$30 before Google catches on. They will close your account for fraud and your name, physical address, web address will be banned from Adsense.
I know that google strictly forbids it but what if...