Older Barracuda become very territorial and will swim right up to your face to check you out when you cross the boudary of their turf.
I had one play games with me for 100+ yards swim back to the boat. He'd dart at me, I'd shake my spearpole at him and he'd dart out of sight, only to return and do the same thing again and again all the way back to the boat.
I've noticed they seem to like hanging around the anchor line. The only time I've heard of them being agressive is when divers are spearing them or hitting them with reflected sunlight.