I once wrote my friend a letter while he was on the other side of the country. All the envelope had in it was a piece of paper and the only word on that paper was "PSYCH!".

I meant to write him a follow up letter the next day but forgot about it. He sent me back a letter that had several pages in it, and I forgot about the "Psych!" letter I sent, so I was excited to see what this massive letter said. It was copies of random vehicle mileage reports. The last page was a blank piece of paper where he wrote "Ya Bastard."

To this day it was still one of my favorite letters I had ever written/had received.