overtly bad pairings would likely be things that are way opposite of each other - that tuna tartare with a big, dense, and inky Napa Cab or Aussie Shiraz would strike me as a little odd. Those wines would just drown the flavor of the fish (and it can be assumed that this "bad pairing" also applies to other light fish items like crudos or even some sushi). I also don't like wine with most anything that has a lot of spicy heat - that alcoholic Cali Zin is going to elevate the heat, while a light and fruity Vinho Verde would just get completely lost in the same way that a similar wine is going to get lost next to that fat ribeye steak.
Even so, I've probably had similar combinations at home, and the most important thing is the enjoyment.
Every once in a while, there'll be a wine that just really sings with a particular food item (Piob's beef stew and a rustic Chianti seem really ideal. Edit: and looking back, the Brunello I mentioned in my earlier post about beef stew is made with predominantly the same grape and is from the same region as Chianti), but so much is in the eye of the beholder. Except for Bachelet Burgundy - everybody is required to love his stuff, and if they don't, then they're heathens.