Report a preset
Tap the … menu on the preset, choose Report, pick a reason and confirm. It disappears for you straight away, and it is hidden for everyone once several people report it. Reports need you to be signed in with Google, so that one person cannot make several accounts to hide someone else's work.
Block someone
Choose Block user from the … menu on any of their presets or comments, or on their profile page. You stop seeing their presets and comments everywhere in the app. They are not told. To undo it, open Blocked users from your account menu in Community (or from the ⋮ menu when you are not signed in).