Blood on a skirt ruined my Rainbow Brite cosplay... thankfully I had only planned to wear it the two times I was able to!
My third attempt at Zelda's dress was ruined by the hangar I had the dress on... I never thought that a plastic hangar could put a run in fabric but it did and I couldn't even patch the area since it just looked terrible. Attempt #4 at that stupid dress to come yet! Maybe.
Princess Bubblegum (Adventure Time)
Marceline (Adventure Time)
Suiguintou (Rozen Maiden)
Twilight Sparkle (Princess - My Little Pony)
Rest to be decided.