Until I started a new IT position a few months ago, I had never heard anyone refer to the backslash as "whack." Luckily I was able to pick up what my coworker was saying through the context of the conversation so I didn't look like an idiot, but it made me wonder what the origins of the "whack" term are. Google confirmed to me that this isn't just something he made up and that it is a semi-commonly used term, but I didn't see anything on its origin.