Interestingly, stingray spines like this feature prominently in Mayan blood-letting rituals (and burial caches), where the Ahauob (royalty and nobles) pierced themselves in the genitals, tongue, etc. to provide blood offerings.
Of course, the live stingray also comes with a venom, so the stick of the spine is accompanied with an injection of a neurotoxin which has particularly nasty cardiovascular effects. Most stingray incidents involve waders stepping on them, so the wounds are typically in the extremities and are only rarely fatal (I think one report said that there had only been three confirmed stingray-related deaths in Australia) ... however, Irwin got hit right in the chest, which is likely why this ended up killing him.
Ain't I just a font of morbid curiosities?