Why do smokers do it?

I was at a majlis bertahlil last night and I was sitting under one of the tents available. As everyone finished eating, some guys were lighting up their cigarettes and smoking away. Why are some smokers selfish and irresponsible by lighting up while in the company of people who don't smoke? Why do they smoke and blow their smoke in your face? Isn't smoking prohibited when there are more than three people in an assembly?