When an especially smug Mac user gets owned in a PC vs. Mac debate. Usually, they deserve it. The saying is based off of Apple's tendency to name its products with the letter i in front of the rest of the product's name.
Mac Owner: "My laptop is so sleek. You just have one of those soulless conformist boxes."
PC Owner: "How much did you have to pay to get that wireless card installed at the Apple Store? I just bought mine at Best Buy and plugged it in myself."
PC Owner: "You just got iOwned."