No idea what they were thinking. Bacon goes with eggs and hamburgers, not ice cream.
I tried the new bk bacon sundae and it was... pretty nasty, icecream made the grease from the bacon clump up and yeah... not a good taste at all in fact I felt like I would throw up from another bite.
There's good bacon treats, and then there's the "Oh my god what the hell were you thinking/drinking when you thought of that" bacon treats that I've seen. The sundae falls into the latter category.
Other notable "good" entries into the first category are:
*Chocolate covered bacon
*Maple Bacon bars (don't knock it until you think about it, you eat bacon w/ your syrup-ed pancakes right...?)
What did you say about bacon? We fighting meet at the swingsets
What did you say about bacon? We fighting meet at the swingsets