"Einige Adjektive verkürzen vor männlichem Substantiv Singular die Endung:
malo mal schlecht
Aber wie sieht es aus, wenn kein Substantiv folgt?
"As a native speaker I can say that in...
...Spain, "está mal" is used when you're talking about something that has not been
done correctly. "está malo/a" is used when you're talking about someone who is sick
or ill, or when you're talking about something that is in bad conditions, e.g. "la carne
está mala" (i.e. you can't eat it because you may get sick)
...Latin America, it depends on the country, but in most of the them you have to use
"está mal" in any context. thus it is wrong to say "está malo". Moreover, the term "malo"
is used together with the verb "ser" (e.g. es malo, son malos, etc.). if you use "malo"
attached to the verb "estar", you REFER TO A PERSON who is not used to being rude,
but who is now behaving in that way, maybe because he/she is having a bad time."