Here a way to get this achievment Easily.
1.Complete coop with someone.
2.You and your coop partner create a new xbox live account each / use a 48 hour trial on 2 seperate accounts.
3.You play the tutorial with the other persons 2nd account.
4.They switch back to normal account and you switch to second account.
5.You then do the tutorial again, opposite of 3.
6. You both should have the achievment with normal accounts which did 1.
Make sure that you are Friends with the other accounts when you do the tutorial with them,Or you will not get the achievment.