It sure is an unusual problem that your friends experiencing. As he has mentioned that it is not intentional one may guess that he is uncomfortable in such situations. Sometimes one is not sure how to deal with difficult situations and laughing is almost like a nervous reaction that he may have.
One advice that may help him is to try and think of the gravity of the situation that he is in and the likely impact of this on the people around him. If he fails to empathise then he can try and recall some incident in his life where he might have felt a negative emotion and this should help him be more sensitive to the situation.