Harry had composed half a dozen different letters to the Weasley Twins. This was important, and they didn't generally do important. They did mischief, and chaos, and deeds that were crazy after the fact. So, Harry needed to make this count. And, to persuade the Weasley Twins, you had to be both clever and fun.
Harry had eventually (over an inkwell's worth of ink) decided on the excessively formal. For a boy with holes in his pants and tattered trous, it was a funny thing. Snape would have sniped, An Arrogant Thing, but that would be why Harry would NEVER use this formality with the crotchety, disagreeable old Potions Master.
Dear Terrible Twins,
In my time of need, nay of desperation, I write to you, for you have the answer to my most fervent prayers.
I have read in your missives of multifarious experimentations, large and small, bright and black.
What I have need of is one of your more recent creations - the Cloying Clods. For I have a most devious prank, tuned towards one of the least light-hearted personas within this house of learning.
That is, if they still have the side effect of leaving one with a voracious, nigh unsatisfiable appetite?
I should be happy to offer you a berth in my quarters, should you have need of one after such a long journey from London.
Make haste to me, the schemes I weave are intricate, and the planning must be done beforehand.
Your silent partner,
Harry folded it up again, knowing that Hermione could have added much more folderadoo, but that it would sound more authentic with Harry's relative inexperience. And that the Twins would have conveyed whatever he'd wanted, even if it was half the shop and all the stock of Peruvian Darkness Powder. Perhaps he could get Ron to write to the Twins, asking for some basic supplies? Pranks might not be Harry's expertise, but everyone was looking a bit strained, and perhaps a bit of laughter might come in handy...
Everyone else was fast asleep in their beds by the time Harry slipped up to the Owlry. He didn't especially want to explain to Ron what he was doing writing Ron's brothers.
[a/n: I had planned on putting something completely different here, but oh well. This is what Harry wanted to do, so it gets done. Leave a review!]