How to prevent insults from unconsciously causing negative emotions?
Mindfulness meditation can help reduce the intensity of emotional pain. This study explores this further. Even listening to music may help reduce the intensity of pain.

Source

Christopher A. Brown, Anthony K.P. Jones. Meditation experience predicts less negative appraisal of pain: Electrophysiological evidence for the involvement of anticipatory neural responses. Pain, 2010.  doi:10.1016/j.pain.2010.04.017

David H. Bradshaw, Gary W. Donaldson, Robert C. Jacobson, Yoshio Nakamura, C. Richard Chapman. Individual Differences in the Effects of Music Engagement on Responses to Painful Stimulation. The Journal of Pain, 2011; 12 (12): 1262. doi:10.1016/j.jpain.2011.08.010