And basically the same is with any person saying in any situation that s/he is a good person. OK... maybe you are for most of the time. But what about the dark side which shows itself from time to time.
Anyway... how can we see and/or detect the dark side ?
This is not always easy or at least not straight away as somebody may be a really good actor and/or this negative aspect may be hidden under many layers of good and positive personality. In any case one thing is sure that once you start talking about this topic in front of this person ( and it can be intuitively without really knowing about what is going on inside of this good person ) then automatically s/he will not like you. And of course this good person cannot act in a negative way so s/he will try to act pretending that everything is ok but still s/he will not like you.
But if you somehow continue to bring on this point ( and as I said it can be done intuitively ) the patience of this good person will eventually come to an end and then you may see some explosion of some kind of emotions. It can be anger, hate etc. or simply tears because this person will try to act a role of a victim being hurt by you.
And so you'll see... this is how you will be able to detect the hidden dark side under the cover of a good person. Just be yourself and your true self will automatically expose ( intuitively ) the dark side behind the mask of a good person.
We also have to remember that this exposure is only there to help and assist the other person to see this bullshit. Every person is aware of what they have supressed and allowed within themselves. But still it may be difficult to see it straight away as this dark side could be hidden under many layers and it could have been there for a very long time.
Obviously this exposing is effective in terms of assisting other people. When it comes to me it is rather difficult. But then there are other people who will expose it within me. And all that is needed is to be aware and pay attention to any kind of emotional reaction that arises within me.