Ice Cream and Vinegar
My mom watches Alton Brown, and while she doesn't always like his recipes, she respects his knowledge and is willing to give things a try. One of those things recently was balsamic vinegar on ice cream. Tonight at dinner, sheherazahde and I tried it on a store-brand premium vanilla (I gave a taste to skitten as well).

Out of the three of us, I was the only one who liked it. It was an interesting combination of flavors which I think worked well. I put much more vinegar on the ice cream than Zahde, but she didn't find it improved by sampling a section of her bowl richer in vinegar.

Supposedly, Alton mentioned that while we don't tend to think of sweet and sour as flavors that work together, the Chinese have long had "sweet and sour sauce", which shows they can. I think he's missing a much closer example: Lemonade is almost pure sweet and sour, as are sweetarts. Along the lemonade vain, there is the medieval middle-eastern drink sekanjabin, which is essentially a syrup made with sugar, vinegar, and mint, served with ice water. Sekanjabin has the sweet/tart taste of lemonade, but without tasting lemony. Instead, it tastes of mint and of the origin of the vinegar (imagine that). So I don't think sweet/sour are bad in combination.