Testicular torsion, left untreated for a minimum of 12 hours when I started puking from the pain, that's when I got to the ER. Some anti-nausea and morphine through an IV got me into a ultrasound when the motherfucking resident found the twist and made sure I was on an active dose of morphine and tried to untwist it without anesthesia. Jesus fucking lord Christ in hell, nothing can't undo that pain. (Cue 17 years later I discovered it helped me develop PTSD ).

Right up there was a pneumothorax where the ketamine didn't work and the pain meds were pretty shit when they put in the emergency chest tube. You know, scalpel through skin, muscle whatever is between ribs and plueral cavity. I was tripping balls so I felt the stabbing while I left my body and observed getting cut into (probably from the mirror light above me). Also contributed to PTSD I learned.

Not so bad as those but still almost made me puke from pain was an EMG on my hand to diagnose how bad my carpal tunnel was. The neurologist went straight for a nerve I guess and is was a lightning bolt of pain that didn't stop until he took the needle out.

You're probably thinking now "Jesus you've probably got a high pain tolerance" and no, quite the opposite actually. Prior to some intense therapy, pain in any amount always led to panic attacks, as my brain had made a leap from pain = bad to pain = literally dying.