Why does the dislike number start with a ~ ?

It is a guess, not YouTube's own count. YouTube no longer shares how many people disliked a video.

SkipTube works it out from its own people. It takes YouTube's like count, and the share of dislikes among the votes SkipTube people cast on that video. The result shows with a ~ in front.

The number only shows once SkipTube people have cast 10 votes on the video. Before that, the dislike button shows no number.

To vote, you need a SkipTube account or a YouTube sign-in. Your votes help the guess. See The Watch screen.