While having conversation, make sure that he is facing you. Otherwise it shows that he is not interested. You can also read his mind with his hand gestures, if he manages to touch you gently then that means he is interested. But if you felt that he is stiff it shows that he is very uncomfortable. Don't hit the hottest temper by being insensitive. If he is not in the mood, that does not mean that he is not into you. Most probably he just had a bad day at work or his team loss. Whatever it is, don't fret about it too much instead try to write down what you did that night so you can see whether you commit something wrong.
You have to remember that everything is a learning process!