I got a little sting from my torch coral once, it was soo weird. A small whitish spot appeared on my finger afterwards. I was scraping the coralline algae near him and felt a pricking feeling. Normally clownfish are worse than anemones are for hurting you :P they really won't hesitate to "bite the hand that feeds them."
In terms of dying, I hope nobody would die from any corals/Nem's.
The most painful thing I can think of that might come about as a result of having a saltwater tank is probably a fireworm sting. Well, techincally not a sting. They have thousands of tiny spines that slough off and stick in human skin, causing intense burning and after effects for 3 weeks. I saw a picture of a 3 foot long fireworm caught in somebody's sump on canreef once. Gruesome >.<
Does that somewhat answer your question?