Anything that is superficially popular, especially to those who do not understand or are unable to appreciate a superior alternative. While originally pertaining to alcohol, ("I don't like vodka, I'll just have a jello shot and giggle later about how drunk I am,") the term "Jello Shot" can be used to describe any cheap, plastic piece of crap that achieves a cult following without any real merit.
The PT Cruiser is a jello shot. So is the "New VW Beetle," the Chevy SSR and HHR. You see them at car shows, but nobody really gives a rat's ass. Certain pop stars are also jello shots, exceedingly popular among those who have no taste. Basically, any product that causes a ton of people to spend too much money on some sort of girlish, cheerleader-touted, one-hit-wondery piece of crap is a Jello shot.