There's a difference

1. When to use "That's mean"

Situation: You're walking innocently, floating like a butterfly when I come over, slap you on the face, trip you, beat you up and spit on you.

That's when you say "Hey! THAT'S MEAN! Why'd you do that to me when I did nothing to offend you?"

2. When you can use "That means"

situation: Someone asks you the meaning of a word and you're trying to explain it.

You say "Oh, that means .... bla bla bla"

In this situation, you ABSOLUTELY SHOULD NOT USE No.1: That's mean.
eg: a: What does the word 'mean' mean?
you: Oh, that's mean evil.

The example I just gave is WRONG WRONG WRONG WRONG WRONG.

the literal translation when you use the example I just gave is: "Oh, itu jahat jahat"

when you want to say "Oh, itu maksudnya jahat"

So instead of saying that, you should be saying "Oh that means evil"

please take note.

kthxbye.