I don't quite have the time/patience to hand-spin enough nettle string for a whole shirt, though that would be the excellentest thing, and if ever I have an engrossing 156-hour cult tv series in a boxed DVD set that I have to watch for, erm, work, then I Will Do It (nettle shirts for all!). In the meantime, I figured a nettle coronet might be do-able, King Lear style:
Alack, 'tis he: why, he was met even now
As mad as the vex'd sea; singing aloud;
Crown'd with rank fumiter and furrow-weeds,
With bur-docks, hemlock, nettles, cuckoo-flowers,
Darnel, and all the idle weeds that grow
In our sustaining corn.
Once you have a goodly supply of nettles, you remove the leaves (good for eating if from a reliable source, or composting if not), and then peel the outer fibre - the epidermis - off the stalks in strips as long as you can make 'em. I kept my gloves on for the leaf removal, but didn't worry too much for the stem-skinning.
And then let them dry over night. And then, the next day, take a strip, fold it over in the middle to make a loop and then start twisting the two halves around each other from the loop down towards the loose ends of the fibre. When you're a few centimetres from the ends, you introduce another strip, folded over in half again to make a U-shape, then insert the U into your prior twist, and then ... okay, too complicated. See here for clear instructions on how to make your own personal cordage out of whatever you fancy.
By now, on the "one, two, skip a few, ninety-nine, a hundred" principle of nettle-coronet-manufacture, you will have a length of nettle string. Ta da!
Now, for the super complicated bit: you corner your King Lear substitute, assess her/his mental health and parenting philosophy (you don't want anyone you know to be too much of a King Lear substitute) and then you wrap your nettle crown around the crowny bits of her/his head. Double ta da!