I (and about 9 others) had a confronting encounter with a triggerfish on my very first ocean dive in Fiji last November. This was on a trial dive, pre-certification. The divemaster told us before we entered the water to be on the lookout for the fish, as it was their breeding season and they became very territorial and aggressive (defensive?). On entering the water, we discovered that the boat was positioned directly above a pair of triggerfish hovering above their nest, a depression scooped out of the sand about 6 feet across, about 30' down. The female stayed close to the nest, but the male made a beeline for us, and harassed us for about 10 minutes until everyone was in the water and we had moved out of the area. He then proceeded to tail us, and would occasionally bite our fins. Bit disconcerting for a total newbie to feel something tugging and shaking at your leg! Fortunately no-one was injured, as this sucker had a mean mouthfull of teeth that looked like they'd make short work of someone's fingers. The fish looked to be about 20 inches to 2' long.
Since then I've seen triggerfish in Melbourne, but these guys were only a foot long and very timid.
Ben.