A printable crab and or nut cracker. There never seem to be enough at parties with crab. (yum!)
Although I have not personally printed this, I am told the joint works great!
Edit: I have reduced the plastic required to print this, increased the gap between sliding parts, and better commented the code.
Print with a dense infill and start cracking. By default the part has 0.6mm between sliding parts, so your printer needs to be calibrated.