If a waiter said something like this to a client being an asshole, some restaurants may fire them if the client is "important" enough, primarily because waiters are easily replaced.

But nowadays, a lot of restaurants will side with the waiter on such issues and they're damn right to do so.

I'll add that what you're seeing here is but the tip of the iceberg of abuse that Lennart has to deal with every day. I challenge you to put up with 1/100th of what he's putting up with without "raising your voice" or what have you.