A clueless, nebbish, or otherwise lost individual. A Francine can be of either gender, and has nothing to do with femininity/masculinity. Rather, to be a Francine, one usually must make a dumb or glaringly obvious suggestion, or generally behave in a manner which is more becoming of a slightly brain-damaged garden slug.
This term seems to have originated from the 1984 film, "Ghostbusters." It was coined by Dr. Peter Venkman, played by Billy Murray, in reference to Dan Aykroyd's character.
"I was thinking that maybe for Halloween, we should carve some pumpkins!"
"Wow, way to be on top of the decorating, Francine."