How much we are affected though varies greatly from person to person. Temperament plays a role and also the relationship we have with the person putting out the negative energy.
I know that I used to be greatly affected by the moods of the people around me but I have worked hard to understand where I should be putting my emotional energy. It is not that I do not care. I just do not internalize that mood as my own.
Many years ago I worked for someone who was extremely moody. If he was in a bad mood, then I immediately started wondering if I had done something wrong. It is his mood and energy though, not my own and I have learned to separate.
It is emotionally exhausting to carry around the moods and energy fields of those around you. It is freeing to know where to draw that emotional line.
Sometimes we know where the line should be, but somehow we cannot make that connection with our own behavior.
Empathy and the ability to see and feel a situation from another perspective than your own is an important life skill. It is knowing that difference between empathy and internalization that is at the core of developing an ability to deflect away others energy.
It is at the core of self esteem. It is at the core of a sense of self. We can empathize with others about their feelings without taking on those feelings as our own.
Put an imaginary, protective shield around you. When surrounded by an energy field that you do not want to absorb, imagine it not being able to get through this shield.
It may sound silly, but visualization will help develop better personal boundaries. Understanding and learning about our own personal boundaries helps create a sense of self that is better able to be solid and strong.
image from: http://www.tomokohealing.com/jp/wp-content/uploads/2010/11/energy_healing.jpg