translation

早く寝ればいいのに。
I said this once to my Japanese friend since he's always sleeping so late (like 6 am) and then wakes up at 1 pm and tells me around dinner time how tired he is.
Is that a rude thing to say? Maybe it sounds like i'm scolding?

早く寝ればいいのに。
It depends on the tone how you say it. It *can* sound like mom or elder sister scolding her son/her younger brother, like "What you SHOULD do is go to sleep early (but you don't!!)"

i did put emphasis on the いい　and に, does that make it worse?

Ummm, I can't say it makes it worse. When I said the "tone," I meant to say that if you said it like a complaining mom/elder sister, pouting at the guy, it could sound like scolding... but come to think of it, if you place emphasis on "ii," it would be like "(You know) it would be GOOD if you went to sleep early! (but you don't!)" Maybe it came out a bit strong. Not intending to be nosy, but was there any complaints from the guy friend by the way??

after i said it?? He gave me a face that looked surprised. I was wondering if it was a bad thing for me to say.
I got the phrase actually from my text book, and the way it was used in the dialogue made it seem like something a friend would say to another friend.

The phrase itself is not rude or anything like that at all. Maybe he was just expecting you to say "ohhh, that's gotta be a tough life" instead of giving him a simple, clear suggestion like that lol. I think that was more like it :)

haha, I don't know how I could tell him "that's rough" when he can go to bed whenever. He doesn't have a lot to do before school starts.. so he watches Japanese you tube all day. Funny though cuz he said he came here early to study English... :-p
Thanks though.

btw...how else can I use のに in a sentence? I'd like to sound more natural when I talk.

"...no ni", in the middle of a sentence, works as a conjuction like "... even though."
- Takusan tabeteiru no ni, kare wa futoranai. (Though he eats a lot, he does not gain weight.)
- Nihon ni nando mo kita no ni, Kyoto wa hajimete da. (Though I've been to Japan many times, this is first time for me to be in Kyoto.)
- Tomodachi no denwa bangou wo kiita no ni, wasurete shimatta. (THough I got my friend's phone number, I forgot it.)

"...no ni." (at the end of the sentence) has essentially the same meaning, adds something like "..., nevertheless," "but...," like in the earlier sentence "(you should do something) but you don't."

So it's used at the end of those suggestions/recommendations:
- Hayaku nereba ii no ni. (You should go to bed early.. (but you don't.))
- Motto nihongo wo benkyou sureba ii no ni. (You should study Japanese more... (but you don't.))

Another example: suppose you are talking with your boyfriend and you are arguing about where to go for the weekend. The boyfriend decides "OK, we're going to Disneyland!!" because he wants to. You might say:
- Demo watashi wa ikitakunai no ni. (But I don't want to go... (but you don't care/you want to persist and go.))

Another example: suppose you are having a party at a friend's place, and you run out of... let's say, beer. One guy who is already quite drunk gets up says "I'll go and buy some more..." you try to say "I'll go" but the guy persists and goes out stumbling; you might mumble:
- Watashi ga iku no ni... (I'd gladly go.... (but you don't/he doesn't let me).)

If you see a pattern emerging, it's a "but..."type of sentiment about what is happening in reality, and *could* sound a bit nagging in some instances :).

thank you.
Yes i remember using it as "although this is the case... contradicting case.." But we didn't really practice using it at the end.
I feel the implication fits the Japanese culture well, as they don't need to be as direct as Americans are. It's interesting how quickly they get what you mean without even saying it or needing to know why.