Not your poem, unfortunately, but I remember this one from my childhood - Tender-handed stroke a nettle, and it stings you for your pains. Grasp it like a man of mettle, and it soft as silk remains.
It's true Dundern,
If a nettle brushes against you it stings, But the palms of your hands being thicker, means that you can pick leaves off a nettle with impunity.