Got your pantyhose on? Sure ya do! After Japanese nerds began covering their cars, motorcycles, and bicycles with geeky images, it was only time before they moved to stockings.
"Ita" (痛) refers to "pain" in Japanese, and the cars covered in geeky stickers were originally called "ita-sha" or "painmobiles" due to the pain they inflict on the owners' wallets and the pain they inflict on everyone's eyes. Since then "ita" has come to mean anything that's covered in nerdy images.