Humans are inherently a very complex species. Multiple emotions hound our minds at one single point in time. Every single person we meet is a mix of different shades of gray. Hence, the lines of differentiating 'good' from the 'bad' are majorly blurry. But, there are always cues. 

If you are confused about somebody and wondering whether they are truly a nice person, be my guest, this Reddit thread has got your back. People are actually revealing subtle signs to identify whether a person is all nice and kind as they present themselves to be.

1. "When they always "playfully" insult you, but can't handle any criticism about themselves at all."

MarcusDasom

2. "If they are being overly corrective and/or policing people for their real world behavior. They feel like they've found a cheat code to being rude if they can disguise it as being nice in some other way."

dj405

3. "Niceness is a demeanor, goodness is a core value. But to the intent of the question - Being rude to service staff is the #1 way to lose my respect."

YakkitySmakkityDo

4. "Talking crap about others to get a laugh. You can tell pretty quick if it's mean-spirited."

Otherwise_Ad233

5. "There are usually two types of people, the “it’s their job anyways” and the “no need to make their job any harder.” For example, if someone just dumps their trash wherever at a restaurant, store, etc. because “it’s someone’s job to clean it up”, they’re probably kind of a jerk.''

Wellokayythennn ·

6. "They are unkind to people they don’t believe can do anything for them."

TerribleAttitude

7. "Nothing is ever their fault, they always find some way to shift the blame to others."

-eDgAR-

8. "They have no humility. Everything they say and do is meant to subtly inform you of their intelligence, abilities, competence, achievements, connections, etc."

Onlyhalfjewish

9. "How they treat animals, usually a good way!"

a_well_travelled_man 

10. "They neg you, and it’s not “friendly ribbing.” It’s just subtle put downs meant to make you feel insecure and inferior."

chibinoi

11. "They become an insufferable jackass when faced with a minor setback. Anyone can appear nice when things are going their way, but it's harder to hide your true self when you're stressed out."

DeathSpiral321

12. "How they treat disabled people."

geico_fire 

13. "If they always tell their side of the story like they can do nothing wrong and how everyone hates them for absolutely no reason. They’ll sometimes also plot to f**k people over for absolutely no reason. That’s signs of a straight manipulator."

thepenguin575757 

14. "How they act when you mess something up on accident. If they’re nice, they’ll let it slide and be understanding, but if they’re an a****le, they’ll make a scene. And if they’re just hanging with your group, they’ll just be really condescending and won’t let it go."

thepenguin575757 

15. "Unapologetic when “joking”. I have a pretty sarcastic and acidic sense of humor, however I’ve learned to not be mean, and actually stop and apologize when I cross a line I didn’t mean, whether the other person says anything or not."

Teyakko 

It is crazy how a person can be so exceedingly charming from the outside, but the further you get to know them, the farther you wish to get away from them.