At least nettles relly only cause problems where they brush up on you!
Try looking up Poison Ivy or it's cousin Poison Oak, they have a nasty, clear coloured oil on their leaves (urushiol) that if you are allergic to creates quite the rash. Bonus to that is that you may have it on your hands and transfer it to other parts of the body unless you wash it off with something that will remove the oil (hardly likely while you are out riding). Mate was not happy to find out later it was on his hands when peeing on a ride! Finding out you had it on you and are getting a rash can be 2-3 days later. Sometimes I wish I'd not moved to the US!
STL
Nice almost as much fun as the following:
[list=1]
[*]Make Chilli
[*]Eat Chilli
[*]Decide to go out
[*]Put Contact Lenses in
[*]Cry…
[/list]