Qual è la differenza tra the usage of mau e ruim with nouns ?Sentiti libero di rispondere con un esempio.

@aysthekitten As you can see, “mau” is commonly used before the nouns. It usually follows a noun to caracterize it.
For example: “mau pensamento; má (feminine) pessoa; mau olhar (olhar is originally a verb, but in this case it was “noun-transformed”, but forget that if you don’t understand, I just couldn’t think of another example)

Its opposite, “bom”, follows the same pattern: “boa pessoa (feminine); bom pensamento; bom olhar (not in the sense “you see well*, but something like “your eyes transmit good energies”

*”you see well” would actually be “Você vê bem” (“bem” is an adverb, it follows the verbs, its opposite is “mal”, with an “L”, not “mau”)

However, “ruim” follows another pattern: it comes after the noun. Ex.: “Pensamento ruim, pessoa ruim”

It is all arbitrary. There isn’t much sense in it.