Snide means insulting or contemptuous in an indirect way. If your friend is wearing too much purple eye shadow and your other friend whispers to you, “What? Was she in a car wreck?” that’s a snide comment.
Snide remarks are the kinds of things people say with a sneer on their face. When you leave a movie theater and your friend says, “I can’t believe someone was actually paid to write that screenplay,” he’s being snide. Instead of saying, “That movie was terrible,” he's expressing his disdain in a more underhanded and indirect way.