Funny way to fold a letter
Here's what we want to achieve :

Step 1 - Get yourself a normal sheet of paper (216mmx279mm or
8,5inx11in) Write your letter and then you're ready to fold... I advise you to
practice this before folding a real letter though because you might need some
practice...

Step 2 - Fold the top of your letter at 45 degrees. You will
get a big triangle and a little rectangle which is the bottom of your letter.

Step 3 - Fold the whole thing in the middle, so the right
bottom corner of your letter joins the left bottom corner.

Step 4 - Turn the paper around.

Step 5 - Fold the part that is not a triangle. To get the
right lenght of paper to fold, just fold the part that was your little
rectangle in the beginning. If you fold less than that, you'll get some ugly
little thing in the end. If you fold more than that, you might not be able to
close your letter in the end.

Step 6 - Fold your paper again, so the last thing you fold
gets "inside" the letter. You'll see a fold appear. So, you'll have
a little triangle left, and your letter will have a fold that goes from a
corner to a bit more than the middle of the letter.

Step 7 - Fold the little triangle over the letter.

Step 8 - Now you'll see you're able to enter the tip of the
triangle inside of the fold you could see before.

Et voilą!!! You got a letter, folded in a funny way. People will go "Huh? How the heck did you fold that letter?" :P Have fun!