the worst sting (bite?) I have ever gotten was in Costa Rica on a service trip when I got stung by a hornet on my collarbone. I have gotten bitten/stung by many things in my life and I can say that was the worst.
As a side note, Have any of you had a reaction to the catatpiller of the brown tailed moth? My mom (as well as many of my siblings and friends) have had terrible reactions to the furs released by the bug and it caused a long lasting welt-like reaction. Yet when I asked my friend in medical school, they had not seen the bites before.