A Little Gestural Mistake Proves A Neglect For Someone!

Consider the following examples for a while:

a. You are on your way and you come across a mother with her sweet toddler child. You start cuddling him/her and ignore the mother totally (no eye contact)
b. You meet someone you know on your way, with his or her spouse. For you, the spouse is a stranger and you had no contact before, with him/her. You talk with your acquaintance for a pretty long time and ignore the partner standing beside him totally (no eye contact).
c. You are on your way and meet someone you know personally with his/her child. You talk to your friend for an hour or so and ignore the child totally.
d. For the fathers or mothers, when one of them come from outside and say hello to only kids and ignore the other members at home.
e. You are too busy on phone/Face book/ surfing to talk to your spouse, children or parents.
How can one do that? If you are thinking so then it is your lack of such experience. This happens with many people in one way or the other. There could be several other examples to quote in this regard that look bizarre, but are very much true and critical indeed. One can do it consciously or unconsciously, but it obviously does not look good and one cannot consider such examples as the best manners precedent.
If you have ever encountered one of such incidents, how would you describe your feelings and what will be your reaction to that?