BLUE TONGUE SKINKS

Today when I went to pick up my little guy (an eastern blue tongue) he threatened to bite me when I got close, this is the first time he's done this since I've had him should I be concerned?
My mother rescued him from one of our cats as a baby and we raised him since he miraculously survived missing a part from his body, which has since healed over. I've been handling him for a little over a year, hand-feeding him and occasionally letting him roam around inside and in a large potted plant outside. He's been docile towards me and my family since about 2 months after we rescued him and I've been taking very good care of him, I'm worried that he may have injured himself playing around in his tank but I can't see any visible injuries. I carefully picked him up after he threatened me twice and he seems fine now. I'm worried about him though, it was such a contrast to his regular behaviour.

First off, it's so awesome of you to have saved your little guy; I'm sure he appreciates it very much.

The nippy behavior could be a lot of things. He could have been startled by your hand or he may have just been saying that he didn't feel like being social at that moment. I have a rather large Northern, and when he's not feeling up to leaving his home, he's an absolute devil.

Just by the by, beginning brumation and going into breeding season are a couple of other things that can really affect a bluey's personality. I'm not sure if it's breeding season yet in Australia, but in the States, my boy's had quite an attitude since he properly woke up.

My BTS used to be, quite honestly, the worst case of a grumpy skink I've ever heard of. After months, he finally calmed down, and I haven't been bitten by him since. Despite this, he does get huffy with me from time to time, even though I try my best to approach him slowly.

Did you move too fast, or was your hand coming from above? It could've just startled him, and made him react instinctively. Especially since after you picked him up, he was just fine, that leads me to believe it was just the way you approached him that spooked him.

They have mood swings just like we do, at least mine do sometimes! Some days one of my Easterns is scared to death and runs for his hide when I walk by his cage and others I can scratch his head while he has breakfast. Here in the states their 'season' is coming to an end and they're behaving normally, well almost, again. Noticed similar with my northerns, although they don't bolt for their hides, but they are older.

What setup do you have for it and what do you feed it and how often?

In Australia it is illegal to take native animals from the wild and keep them, even for rescue. If you come across an injured animal you can keep it safe from the threat and immediately phone WIRES or equivalent in your area. It's possible they could have treated it and released it, legally.