Fishing line cutter in the style of M57 claymore detonator. The shape of the detonator is almost perfect for this purpose, since the lever serves as protection for the blade so you can't cut your fingers.

To finish the build you need two 18mm M3 screws and utility knife blade (such as Stanley or similiar).

I suggest to print the Guard.stl from PETG for added strength. The rest can be printed from PLA.