Recently, not as bad as the one below, going to the dentist for four fillings (they had to sedate me and gave me to injections to numb my mouth and it still hurt like hell and the sedative did not help at all).
Much more seriously:
One night, several years ago now, when I was about 16/17, my brother was 19 and my cousin was about 11/12.  Me and my brother took my cousin out to this park until 8pm and then walked her home (school night).
After getting her home safely, my brother and I headed home and ran into an old friend we knew from when we were younger.  He walked us home for a bit and then told us if we tried to run he'd kill us.  He then started threatening our family and said some very hurtful things and warned that if we tried to call out for help then he'd kill us.
We were just a few streets from our house when I turned around and saw someone walking towards and then the guy threatening us attack my brother.  He punched him in the side of his head and he just fell down.
I honestly thought he was gonna die and I've never been more afraid in my entire life.
Anyways, happy ending just to cheer me up, we got home safe and the guy that attacked us got his head bashed in (he lived though) and was fined for it.