I really didn't understand your first sentence.
The word "impudent" means that you are loud, brash, bold and cocky while being impolite. It means to "have an attitude" and does not really fit with "not greeting friends". Maybe "uncouth" or "rude" is better - these mean not civil or impolite.
I'm a little uncouth because I don't often greet my friends.
In the second sentence, the word "they" is ambiguous - it could refer to either the people or the parents. A better phrasing is:
I execrate those people who, when they have grown up (or "become independent adults"), abandon their parents.
"Excoriate," "censure," "denigrate," and "vilify" are some good verbs to use, if you ever talk about such people..