People character's speak so much about them in such a way that what they exhibit out of their characters can be used as a means of judgement regarding the kind of life they are living in the society. The wall has ears, the leaves in the bush has ears and hidden things are exposed without the consent of the power that caused it to be hidden. 
Some eyes might be seeing you, counting you to be something you are not just because of the impression you made when they first encounter you. The case is that you acted wrongly at the first place, so they noticed  you programming in their mind as that kinda person. 
This doesn't apply  only to wrong attitudes but also to good idiosyncrasies you exhibit among people especially in the context of first occasions. 

I could remember having a conversation with my mentor in school, we discussed extensively on the issue of the impression people have meeting with new people. He told me that there is no much mistake about the impression that people have when it comes to meeting others the first time.
To some extent saying that there is no much mistakes about first time impression might be wrong because there are people who acts depending on the situation at that moment which means that the character they show off at that time might not be their true character but they acted that way due to the fact that something pushed them. 

Imagine being in a bus where passengers are making a noise so loudly especially when there is no need for it, they are just disturbing your peace for no just purpose. What will be your impression towards them. Is it going to be bad or good impression? the answer is left for you to give but probably i guess it would be a bad impression. Secondly , how would you regards such passengers when you meet them again? If you are a kinda person that doesn't admit such idiosyncrasies, you will probably not like to meet them again.
The reverse example implies when you meet people you like and the give good impression. You would want to meet them again because seemingly they would contribute positive things to your life and also you would also like to relate with them.

To conclude, people's first impression matters a lot about you. so it is always mandatory that you should be nice to people when meeting them the first time.