It's rude to comment on someone eating alone.
Karl takes his wife out to dinner and sees a guy eating by himself at the next table.
Karl wants to say something to the guy.
Karl asks the guy if he knows what's good to order from this place.
Karl laughs and asks the guy what he did to get stood up.
The guy gives some advice and is pleased to have had a small social connection.
The guy gets embarrassed and feels put on the spot and feels awkward during his meal.