I looked it up online and you can read about the expression here. It's not just Dad's! :)
Anyway, a few weeks back we were having family photos done in a park. The kids were looking for cicada shells on the paperbark trees so I went to help them collect, and then I got all excited. I yelled for Dad and hubby with his phone. Surrounded by kids, and I yell, "My God, Dad, get over here. There's a blue-arsed fly."
Needless to say the mothers, my sisters, sighed with exasperation ... but Dad and Mr E came at my call. Dad as excited as me, and Mr E handing over his phone so I could get a photo.
I think it's a blowfly, also called a bluebottle. But according to my more extensive look at websites and books, it could also be the Snail Parasitic Blowfly - because of those white dots. It seems that they are indicative of that species (see here) - although I'm not sure it's right. If you look at this gorgeous shot on the Australian Museum site here, it doesn't look half as stunning.
So, yep, me and my good IDing! I'm calling it a blue-arsed fly :)