I have taken a few of a grey reef shark. 6th most aggressive shark in the world according to shark week. Also been surrounded by about 7 black tips at the blue hole in Belize no pics as I didn't have my camera at that time. It is pretty amazing and a heck of a rush to be that close to something that could rip you in half if it wanted to.
I lived and worked in the Florida keys and have had lots of shark encounters. Generally the reef sharks we saw weren't all that intimidating. Mostly Bull's and Black tips. I followed a pair of 15' Hammerheads around on Mollasses reef for 20-30 minutes once and they had no real interest in me. The one time I really did get shook up was a couple hundred yards back behind the reef I was Lobstering around a good size coral head. I had already put maybe 5 or 6 lobster in my bag and was half way under the coral head reaching for more. I felt a series of sharp tugs on the lobster bag, at first I thought it was one of my buddies sneaking up and messing with me, but then I looked down to see a 3-4' black tip shark pulling the bag off my belt. He got the bag loose, the lobsters in the bag were grunting and making a hell of a racket, and as I followed the little bastard to try to get my lobsters back about 4 or 5 of his little buddies showed up, and they all started fighting over that bag of Lobster. It was truely intimidating, these little bastards were zipping and zooming all over the place and I could hear the crunching and the clacking of thier teeth snapping as they tried to get at the lobster. At that point I decided they wanted those lobster a hell of a lot more than I did. I swam back to the boat watching my 6 the whole way. I've been in the water with a lot of big sharks but never had the fear like I did with a gang of little mean black tips that day.