since we are on the subject of Coffee, LOL...
We recentless switched our house coffee to decaf, but, I have still been using it in my garden, and in my potted plants.
I also mix in pulvarised egg shells.
This is mostly because the earth that I mix it with comes from my yard, which is nutreantless.
My rosemary (potted) is doing quite well with this mixture, as a plant, and I do not have slugs (eggshells perhaps helped this?).
My garden (mostly flowers and some peppers) also have about a half inch to an inch of this mixture on it, no slugs, not really anything eating them except for the occasional aphid on my roses.
It did, somehow, make my potted mint grow way faster than I expected it to, and the roots basically strangled it out before I realized what was causing the death of the the mint, and obviously, before I decided it was time to transplant it.
Mind you, I really only started heavy gardening this year, and I plan to get rid of most of my flowers and just start dealing with edible plant materials for next year. So, you can't really take my word for Bible here, because it could be other factors that keep the slugs away, maybe I don't have anything that they want...
Hope this helps though