The Collaborative International Dictionary of English v.0.48:

Upsetting \Up*set"ting\, a.
   1. Conceited; assuming; as, an upsetting fellow. [Scot.]
      --Jamieson.
      [1913 Webster]

   2. such as to disturb the self-possession of; unnerving;
      causing mental distress; as, the sight was an upsetting
      experience.
      [PJC]

WordNet (r) 3.0 (2006):

upsetting
    adj 1: causing an emotional disturbance; "his disconcerting
           habit of greeting friends ferociously and strangers
           charmingly"- Herb Caen; "an upsetting experience" [syn:
           disconcerting, upsetting]