When it stop to matter

I'm known to be sensitive. Take things to heart, be hurt by the little things people say or do. Later on, I learnt that it's a waste of energy to let people that you don't care about hurt you.
*
Now, when things get crappy at work, I laugh it off. Because I felt it's worthless to be emotionally affected by things that do not take first priority in my life.
*
The other day a friend at work shouted at me out of anger. I shrugged it off. Later, I wonder why didn't it hurt? Have I never thought of him as a friend? I suppose so..
*
Or am I just getting colder as a person each day...