OUCH!
I've been doing some yard work and finally set myself to clear out a large patch of unattended growth along the side of my house last week. I spent about 40 minutes hacking and picking up scraps that had been growing unfettered for the last two years. It was a mess and still is as I haven't finished the work, but I had filled up my trash can and had to stop.
About two days later my legs looked like a war zone. Red, blistered, and itching. I have my suspicions that in my side yard there is a substantial amount of poison ivy. This suspicion was reinforced when I did some more work on my yard this weekend and got a fresh new patch of rashes. I had always assumed that I was immune to the effects of poison ivy, much as I am immune to every other poison known to man (iocaine powder, etc.), but I have since learned that resistence to poison ivy can lessen with age and continued exposure to it (unlike iocaine powder). So now the warzone that was just my legs has expanded to my arms and chest. I am even now resisting the urge to roll around on the floor at work. It's not that I haven't done it before, but my pants are freshly pressed and I think they've still got another use in them.