We’re not good at it today, however there ate at least a dozen common anti-pattern events that should be filtered by relays.

One example is does an existing reaction event exist from this pubkey for this event.

Events with multiple root etags.

Reactions with multiple p-tags.

Metadata events that are not JSON.

Others include DMs with multiple p-tags, as only one person can read - however maybe DMs mentions someone. Either way you leak data.

I have a list somewhere.