I was stung by many things, here's a list.
Bristleworm - Cleaning the sand bed from some cyano with my bare hands. Dug my index finger way deep into the sand and it lands on a 6" bristleworm.
The pain was not as bad, but a few mins later it started to ache. Luckily I had a bucket of vinegar nearby, so I soaked my hand in the bucket of vinegar for 3-5 mins to dissolve the bristles.
After I took my hand out of the vinegar bath, it was burning from the bath.
Carpet - Bought one online, I was excited to pull it out for acclimation, dug my hand it to check its foot. Next thing you know it expands from the tips and stings the bottom side of my wrist (soft and thinner skin)
It felt like a bunch of needles going through your skin. Freaked me out as I looked at my wrist it was red and swollen. Didn't think much of it at first, woke up the next day to realize there was a huge purple cluster of bumpy stings.
Took 2-3 months for my wrist to fully recover.
Ritteri - Was rearranging my rocks because the nem kept splitting, so I moved it, only to realize that there was a clone on the opposite side. It stung the bottom part of my forearm.
It was a weird burning sensation, burning under water feeling... Looked like a bunch of rashes, it wasn't as bad as the carpet, but took about 1 month to fully heal. It's not even noticeable anymore.
Zoa - While fragging, I had some zoa juice squirt my eyes, luckily I wear contacts, so it damaged my contacts.
When I removed my contacts that night, I inspected the lens, there was a bunch of micro sized brown and white chunks clustering up on it. I made nothing of it, but glad it wasn't on my eye.
What ever it was, it tends to solidify in your eye and cause excruciating pain.