Good and Bad can be confusing in Portuguese, so I thought I’d lay it all out for anyone wishing to understand the differences. I’m going to lead with ‘bad’.
Bad (mau) is an adjective that means “the opposite of good (bom)”. For ex., mau comportamento (bad behavior), mau patrão (bad employer), mau caráter (bad character). Keep in mind though mau is masculine while má is feminine. Likewise, the feminine of bom is boa.
Mau vs. Bom
Má vs. Boa
Bad (mal) is an adverb of mode, contrary to “good (bem)”. It must be employed together with the verb or adjective. For ex, mal-estar (uneasiness), mal-educado (badly educated/behaved), etc.
Mal vs. Bem
Hope that helps!