I don't know if this falls under idiosyncrasy. I bet it does:

I can 'crack' or 'pop' (depending on your vernacular) virtually any bone in my body (even parts that aren't technically 'bones' (keke you said 'bone')). A short list off the top of my head (moving down...haha):

- jaw can 'pop' repeatedly
- neck
- shoulders
- ribcage -- rare feat but doable
- upper spin through hyper extension (bending backwards)
- lower spin through hyper extension (twisting side to side)
- elbows
- wrists
- knuckles (repeated)
- joints in fingers
- 'bone'
- knees
- ankles
- toes