I’m not sure there’s any definitive way to demonstrate the difference between laughing-with and laughing-at, but I know it when I see it.
Is it just the context of knowing they don’t really like the person they’re laughing about?
How does that work when the context is largely made up of laughing? It gets kind of circular.
The one positive is that people will often just admit that they don’t like the person and it’s not a friendly joke.