1) "you" as a concept: nobody at all can do this.
2) "you" as a specific person: only one person can't do this. Other people can do it.
3) "you" as a group: Nobody in the group (or the group as a whole) can do this.
- I didn't say she stole my wallet. Tom saw it happen and he's the one who said she stole my wallet.
- I didn't say she stole my wallet. You're making up something I never said.
- I didn't say she stole my wallet. Maybe I suspected her, but I never actually said it.
- I didn't say she stole my wallet. Someone stole it, but I don't know who it was.
- I didn't say she stole my wallet. She took it, but for safekeeping after I forgot it at the restaurant.
- I didn't say she stole my wallet. I did see her steal a wallet, but it wasn't mine.
- I didn't say she stole my wallet. She stole my money but left the wallet exactly where it was.
It's a great example of how written speech doesn't capture all the nuance of spoken words. Well, italics helps, but hearing it makes a bigger impact.
(It's a bit more interesting, or at least more example-dependent, in the negative.)