Summary

One way of using up all those failed PLA prints...

Instructions

Collect as much failed PLA prints as you can
Put PLA junk into a suitable metal container. I recommend lining the container with something as the plastic will NOT be removable afterwards otherwise
Place in household oven and cook at about 190c until everything melts down
Laugh insanely as the frustration from failed prints melts away like the plastic
Try and figure out what to do with the lump of remarkably durable and hard multi-coloured PLA you now have*

Personally I'm thinking this would be useful for doing DIY plastic casting... Melt up a bunch of dead prints and cast the plastic into molds for cheap and easy reuse! You could probably also use it in CNC milling, however the texture and consistency may vary...