The grapefruit reference is accurate. I'd describe it as floor varnish thinner mixed with hyper-concentrated grapefruit rind. The interesting thing is the way it doesn't actually smell that bad, but then it starts terrible and gets worse after a few seconds. I'm convinced there's some interesting chemistry going on in there where it degrades into other chemicals as it oxidizes in your mouth.

The only remotely comparable flavor I've ever had is...

...Unicum, which tastes like a cedar chest smells, and I was more than a little afraid would make me go blind.

0/10 for both, would absolutely recommend if you want someone to establish a baseline for "absolute worst-tasting thing ever deliberately consumed that is technically meant to be consumed."