The word "naughty" can have a subjectively positive meaning, especially when used playfully in relation to sex. Example: A man smiles and boasts to his friends, "My girlfriend and I went to dinner and a movie last night, and then we went to her apartment and got naughty." [Variant: "... apartment and did some naughty things."] "Got naughty" or "did some naughty things" would commonly be understood to mean that they engaged in sexual behavior, and the man who said it used the word "naughty" in what he considered a very positive sense.

I wouldn't say it's exactly positive in that way, but it's not particularly negative. It can be said affectionately. Interestingly, when I taught at a senior school in England, the kids were using 'naughty' as skang to mean 'physically attractive'.

'Naughty' is anything that's enjoyable, but that you shouldn't be doing. For example 'I'm on a diet, but I was really naughty last night. I had a whole bowl of chocolate chip ice-cream'. Cake is naughty. Gossiping about people is naughty. Most things that are fun can be 'naughty'. The harder these things are to resist, the naughtier they are.

No, not really, and I would be VERY careful about this because of Neil's comments above.

Not really. We'd sooner use words like "saucy" or "cheeky".