I've had tacos made with cow brains. They're pretty good. A little chewy, but good. There are very few things as unappetizing as a fish that still has its eyes.
The worst thing I've ever tried however, has got to be
Balut. I was dared/tricked into eating it when my family was stationed in the Philipines. The smell alone will burn your sinuses away and if the taste doesn't make you wanna throw up, the crunch of the bones will.