I you are hosting a party and you want it to be fancy-dress, but don't want to mess up your carpet, you could incorporate shoelessness into the theme. There are a number of possible fancy dress themes that would fit:
1950s Sock Hop
1960s Hippie party
Silly Slipper party- get guests to bring the silliest slippers they can find.
Ancient Greek themed pary
Ancient Egyptian themed party
If anybody can think of any others, please suggest them in the comments.