It's really strange that no one talked about this incredible glitch that makes this annoying achievement so much easy. There's a simple way (sure not very satisfying) to get this achievement done in relatively no time and i'll do my best to explain it.
The host has to choose a level and as soon as the level begins the host has to put himself in front of a wall or something that blocks him by proceeding in one way.
After that the other player (the partner) has to push the host against the obstacle (i.e. the wall) by constantly smashing the "x" button... the host will be pushed against the wall repetitively and, at that point, he simply has to exit the level! The host's character will bug while the other player will actually exit the match, making a countdown of 9 seconds starts... As soon as the countdown is over, the game will count the level as completed rewarding you with a "C" rank ('cause you actually "completed" it without picking up any gem).
And that's it, i know it may sound weird cause you finish the level without actually playing it, but some will find it very useful. You just have to repeat this glitch for all the remaining levels. This glitch works with every level EXCEPT THE FINAL LEVELS OF EACH CHAPTER which are the only ones you and your partner will be forced to play "legit" (i think this is because those levels are already time-based so the countdown cannot start). AND IT ONLY WORKS, of course, IN COOPERATIVE MODE.
This is a brief summary step by step:
1) The host chooses a level
2) As the level begins the host puts himself against a wall
3) The partner pushes him against the wall by simply pressing "x" repetitively
4) The host exits the level while he is being pushed against the obstacle (tips: you know when you have to exit when you see the contact between your partner's fist and th body of your character, it's just a matter of timing, just keep trying)
5) The other player suddenly "disappears" and the countdown starts
6) Level completed
I add a video below, use it as a visual support to the written guide. The video has been recorded by my friend Mad Mukka using the xbox game dvr app, sorry for the bad quality.
This glitch has not been discovered by me but by my friend DoneTrash8, all credits goes to him.
If you have any question feel free to send me a private message, if you think there's something wrong don't instantly put a negative feedback but let me know, i'll do my best to correct. If you feel hurt by this solution, remember this is only one of the possible solutions, you don't need to follow it and if you want to do it legit (sure much more satisfying and rewarding) feel free to follow the guide above by Zymotic, which is pretty good