You can report or block someone who uses Vanish Mode inappropriately or offensively. You can report a message for up to 14 days after it disappears, even if you cannot see it anymore. You can also report a message more than 14 days after it disappears, but the report won't include that message. You can also block someone by tapping on their profile, tapping the three dots icon in the top right corner, and selecting Block.