Yep I had an adult maccy that did that to me

. I was sitting on the computer (looking at this site quite possibly) and I had him curled around my left wrist. I saw him move so I looked at him and he half opened his mouth and leaned toward my thumbs knuckle. He half bit the knuckle first (mouth was only slightly open) I continued to watch him and ever so casually he opened his mouth and bit my knuckle and constricted my wrist

. He then let go after about five seconds or so. I hadn't heard of it prior but my current female has tried to do similar once though I realised what was going to happen and stopped her in time.
This guy was very food oriented and had also slammed and contricted my hand while I was moving things in his enclosure.
Don't really know why he did it but thought you'd like to know that similar behaviour has happened to at least one other. Cheers