I've noticed early on that the not so good looking chicks, sometimes if they are with other better looking girlfriend, will tend to act more bitchy towards guys who are trying to get the prettier girls attention. I guess some girls carry their insecurities on the outside and bark at the world, where as prettier girls perhaps tend to carry more insecurity on the inside, which makes some seem reserved or even cold.
Learning how to spot peoples insecurities and thereby letting people own there own insecurities, without taking them to heart, is important in order to be your relaxed and preferably joyous self. People usually accept people who are authenticaly themselves and not trying to please others.