Not all plants you encounter are entirely pleasant. Many of them have defense mechanisms. Here's a poem I wrote recently out of frustration with a plant I ran into.
Darn you Flannel Bush! (Fremontodendron californicum for those who care) I am sure you are the source behind the contact dermatitis on my arms (read: rash). Only poetry can truly express my hatred:
If nevermore should I see
A plant that is so flannel...ly
I shall click my heels together with glee
For my clothes shall be hair-free.
As I wade through your prickly sea
I find a foe in close proximity
For from far away you look so nice
But one close encounter will suffice
To train my brain to re-route my feet
And beat a hasty retreat.
Your big yellow flowers are so pretty
But on your leaves there is a city
Of tiny hairs that stick and prick
Which caused this lengthy rhetoric.
So learn your lesson straight from me
Stay away from that downright wooly shrubbery
Take heed, take heed of what I learn
Or a distinct itchiness you may earn.