I can’t speak with confidence about the legal situation in other countries, but in the US frivolous lawsuits are routinely punished by having the plaintiff cover the defendant’s legal costs plus compensation for their trouble. Avoiding liability in general is still best practice, but there’s no significant risk of liability from actions taken by a customer in the dining area, customers are supposed to be there and nobody could reasonably expect the restaurant owner/management to predict and/or control the behavior of all of their customers. The customer would be held responsible for their actions and would be on the hook for any damages.