So, you've probably heard people complaining that YouTube's subscriber counts have seemed a bit dodgy lately. The folks over at BlackScreenTV have discovered why!
There's a glitch, and it's super easy to replicate. Whenever someone unsubscribes from a channel, it's being counted twice. If people repeatedly subscribe and unsubscribe, the overall total just keeps dropping. Using that knowledge, BlackScreenTV is currently livestreaming on YouTube with running totals of several popular channels, watching them drop. They are currently at -1,554 subscribers (yes, negative subscribers)!
I think I speak for the entire community when I say, "Fix your site, Blizzard!" :~P
Seriously though, this explains why people have been reporting strange fluctuations in their subscriber count. They aren't crazy, despite YouTube's replies that everything is working as intended.