For my daughter's 7th borthday we had an inside-out, upside-down party.  I did the invitations on the computer so they came out in a mirror image.  The children had to put them up to a mirror to read them.  I had a cake made with Happy Birthday written backwards.  All the guests came dressed inside-out and bacwards, with ponytails on their foreheads and zippers and buttons in the back. The guests were then taught their name backwards and given nametags with it on it. We then had cake and ice cream immediately instead of waiting until the end.  Presents were then opened, (some were wrapped in inside-out paper). My daughter thanked her guests (knaht ouy = thank you)  which brought on more giggles.  We then went on to play some bakwards games; Twister, Pin the donkey on the tail, and Scrabble Junior, backwards!  We ended the party with hamburgers, etc.  This was a fun party to plan and was enjoyed by all!