there are many reasons why people laugh, not just because you said something funny, it could also the way you said it and the reason you said it. Look back and check the reason or you can just ask him why, He may not even thinking what you are saying or when you said I drank coffee this morning, suddenly he remembered something funny happened to him about drinking coffee...but asking is the best way to satisfy your curiosity. It all just the way we see things or react.