Speculating in and of itself is not especially annoying to me, but I am constantly annoyed by people who talk during movies, especially in theaters. My mom is particularly bad about this, and will ask questions whenever she's unsure of anything, even when the answer hasn't been revealed yet. Just STFU and watch the movie.

I don't care about talking during games, though, so speculate away. If they're right, so what? You didn't know until you found out for yourself anyway.