Akin to beer goggles, sale goggles happen when you buy something JUST because it's on sale. It may be a terrible product that you will have regrets about once the buzz of acquisition has worn off.
I was at Target checking out the clearance items and came across a purple and yellow striped shirt. After buying it I came home and realized that it makes me look like a "special needs" bumble bee. Darn those sale goggles!