Needs to be done with two controllers.
Have player 1 pick up a paint can and throw it with
to create a stain. Then go pick up the paint can again and walk over the stain so that you drop it and create another stain.
Have player 2 go walk over the second stain you created, and the achievement will unlock.
You don't necessarily need to create the first stain, but I found it easiest to use a paint can for the whole process.