wrong, incorrect, bad

I was all set to say the same thing as mshades; they're more or less a series of stops along a line of judgment from more objective to more opinion-based/emotional.

I would except in the case of spoiled food, because, if you say "the milk is bad," you don't mean you don't like milk. but that's context-specific and idiomatic. You can just say "spoiled" and duck the issue.

just tell them "incorrecto", "que está mal" or "malo" ;-) they will understand!

By the way, I am a native Spanish speaker from Spain who also happens to teach English. I hope I didn't come off as condescending with my answer, I just know that when you get those inevitable "how-am-i-going-to-explain-this" ESL questions, sometimes you just better know the translation in their native language. If you don't, well, just give them lots of examples in different conexts and they will eventually understand. It sounds like a question from a lower level so no need to give too elaborated explanations because they will simply not understand. The above replies were excellent and instructive, by the way.

@ mshades - Thanks soooo much this is perfect!
@ Scyllacat - I will have to mention the milk example, he loves idiomatic expressions.
@ Anita- No worries, I will definitely use what you said above, though my student has a high level of English, it was more a clarification than anything because he is giving a speech soon and wants it to be perfect...well as perfect as possible with his Murcian accent.
Thanks again to all! I will be sure to use all of these on Friday.

I must disagree with mshades, the thing is simpler than that.

There is no moral/ethical judgment when you say Bad/Good, something is bad when it hurts you in some way, and good when you get profit from it.
Right or Wrong depends only on your point of view or situation, and thats it, it can change at any time.
To be correct has to be better, faster or getting better results than other ways to do something, i.e. I do my job in 1 minute, my neighbour does it in 30 seconds, my procedure is incorrect at some point.

"I need more money, changing to a better job will give me more money, this is correct, my neighbour thinks it's wrong, cause I seem happy in my actual job, but cause it does not hurt me, it's not a bad idea."

I disagree, Sharm. Please re-read mshades' post. "Right/Wrong" can cover both "Correct/Incorrect" (which imply factual accuracy, error or mistake) and "Bad/Good" (which imply harm/benefit and sometimes CAN imply moral/ethical judgment -- i.e., "Homosexuality is bad", or "Stealing is wrong").

msshade's post re-read...
Same opinion... I must be thinking latin way i guess...
Im not saying he/she is wrong or incorrect or that his/her opinion sounds bad, every single option depends on where you stand though, but I am sure every single one of them (right,wrong,incorrect..blablabla) has a meaning of its own, i just cant seem to find the exact point they deffer.

What about thinking in terms of levels of "formality": Good/Bad is simplistic, Right/Wrong is familiar, and Correct/Incorrect is formal.

I must giggle, though, and your use of the term, "hard and fast rule" when discussing English... :o)

When learning Spanish I always asked native speakers why things where said certain ways. For example, Obtener vs. Conseguir. They would always say "It just sounds right". I have stuck to that rule and used words that are commonly spoken. It really is unexplainable outside of just colloquial preference why certain words are used over others when they carry similar meanings. When in doubt imitate natives and use the common lexicon.

I feel that bad and good are religious-moral; and right and wrong are secular-moral. Right and wrong can also overlap with correct and incorrect. That's my english though.

Very good site.Thanks