Fox danced past the bounds of good taste last year with “Joe Millionaire,” and good thing it did. “Joe” helped save its season.
   With ratings as bad as last year at this time, Fox is jigging even further behind those boundaries with the new “My Big Fat Obnoxious Fiancé,” a reality show in which a gorgeous woman tries to convince her family that she is suddenly and blissfully engaged to an obese gas-passer.
   It's all very Fox, with the joke within the joke: If she makes it to the wedding with the slob, who she thinks is a fellow reality contestant, she wins $1 million. But unbeknownst to her, the guy and his family are actors hired by Fox to derail things.
   Low concept, sure, but with the potential for high reward.
   As the network most in need of a hit – take away October’s successful baseball playoffs and Fox is a distant fourth this season among adults 18-49 – Fox is taking the biggest midseason chances with “Fiancé” and four other new shows lined up for this spring. 
   By comparison, ABC, CBS and NBC have lined up only one apiece.
   But as Fox found with “Joe Millionaire 2,” reality success is nearly impossible to duplicate. “Fiancé” may share “Joe’s” Monday 9 p.m. time slot, but media buyers agree this one’s an even longer shot.
  “This will appeal to the hardest core of reality fans, but it’s a less accessible show than ‘Survivor’ or ‘American Idol’ because there are less obvious, less if not any, appealing characters,” says John Rash, Campbell Mithun’s senior vice president and director of broadcast negotiations. 
  “The clear attempt is to amalgamate ‘Average Joe’ and 'Joe Millionaire,' but you know it remains to be seen if viewers will accept that.”
   Still, the risk is worth it for Fox. It is 10 percent behind NBC season to date among adults 18-49 and finished last in that demo in November sweeps.
   Monday, when “Fat” airs, is a mess anyway, and the show debuts after the Jan. 19 “American Idol” premiere, giving it some chance of attracting an audience.
   “They’re Fox, so they’re always kinda doing something innovative,” says Brad Adgate, Horizon Media’s senior vice president and corporate research director. “Some work, some don’t. ‘Temptation Island’ and ‘Boot Camp’ didn’t, but the first ‘Joe Millionaire’ and ‘American Idol’ were real hits. It’s just really hard to gauge. If they promote the heck out of it on ‘American Idol,’ that’s gonna help.”