Abcess under my front 4 teeth without doubt. Actually, scratch that, that was the second most painful thing, most painful experience was the actual injection into the abcess. Jesus, that was intense. It didn't last long but...wow. Possibly made worse as whilst I was expecting pain it still caught me off guard. *shudder* Not fun.
It beats appendicitis (wahey!), cameras being put 'places', broken elbow (surprisingly not that painful, more odd) and tearing my ankles/wrists and knees more times than I can count. Actually that hurt quite a bit first time I dd it, once you hit double figures it becomes less of a big deal, more of an 'shit, again?!'.