I don't think it falls under the "injury" part, but it does fall under the painful area.
I found out this weekend that my 5-year old nephew got hold of a can of pepper spray. My sister-in-law in her infinite wisdom used to keep a can of pepper spray in her purse. The only problem is that she leaves the purse in an easy to reach location for her kids. She used to gripe about how they would get in her purse and get the stuff out.
I guess my nephew got out the pepper spray and sparyed it on his chair in his bedroom (I don't know why he's weird). He then got on the chair to play videogames. Hillarity ensues as he starts to scream. I guess he had it all over his arms, chest, etc... They put him in the tub to wash him off and the water causes the pepper spray to activate even more. I guess in the undressing he got some on his pecker

In the end all was well and he fortunately hasn't suffered any future damage.