What do you use spent coffee grounds for (if anything)?

Makes good compost.

Add them to my compost pile, filters included

Applying it directly to plants or mixed into potting soil has very mixed support. It's decomposing cellulose, like any other plant, so it's unlikely to be that bad in any application. Mostly it seems like well meaning coffee enthusiasts recommend it, while mixing grounds into compost appears to be widely recommended even by non-enthusiasts.

The thing I avoid like the plague is getting grounds down the drain. Over time they'll clog drains, collect in pipes slowing flow, etc. and generally be a pain. So I'm careful to get as much out before rinsing as possible without going crazy. I also do not use it in soaps, because soap film plus coffee grounds in your drain is a perfect recipe for those clogged pipes.

I've been meaning to try using used grounds in a cooking rub- leaving them to dry and then mixing them in a spice rub or using them as the rub itself. I'd be interested to see if anybody's tried used versus fresh grounds, and whether there's a noticeable difference.

Compost and mushroom substrate

Right into my city compost bin, along with the coffee filters.

My wife has mixed it with coconut oil or something similar for an exfoliating scrub. Otherwise compost

Like most commenters, I throw them with the filters on the compost pile. But recently I had a dog in the neighborhood pulling out plants in my front garden, and shitting in it. Spreading some of the coffee grounds seemed very effective against that too. I guess the dog doesn't like the smell. So it;'s a win-win because the plants profit from it directly too :D

I rinse out the press pot and dump the water and grounds on a plant in my yard. I try to spread it around amongst various plants but the ones closest to the door get the most...

I toss them directly in my raspberry patch, next to my back deck. They love that shit, and enjoy slightly acidic soil anyway.

I use them with soap to wash my hands when I'm working on cars or anything greasy. Really helps to scrub away the nasty stuff.

Apparently if you do compost with worms, they love the stuff.

At the office, I give them to one of my staff since their family has a large garden/small farm which makes and uses compost.

At home on the weekend, I generally just dump the moka pot puck into the waste bin but sometimes will save it to dry and sprinkle onto the balcony rosemary plants.

I have made a coffee vodka. Saved the grounds up for days, only to realise you don't need much to make it! Left it for much longer than the recipe said, but that was because I wanted a stronger coffee taste.

Paper filters and grounds go directly into the compost bin. We dont have municipal so I have to pay for a compost service but its 100% worth the $40/m to not have a smelly trash can.