How should we punish the people who always fail to keep their promises?

There is that saying, "Fool me once, shame on you. Fool me twice, shame on me." I think you should take some responsibility for believing this person over and over. If you like spending time with and have fun with this person, fine. Let it be casual. But if they lie to you time and time again, you obviously can't trust them, or depend on them for anything serious. Know that, own that, and don't expect anything different from them. Whether or not you completely end the relationship is up to you. You have to ask yourself what so you get from this relationship that's positive. What about this person makes you feel good? You have to doubt how much they care about you if they've hurt you so much. Ask yourself if it's truly worth it?

If this person were really your friend you wouldn't even be asking this question right now. I know maybe sometimes things happen, but if this is happening to you continually I would think it was an issue. Maybe you should limit your time around this person or at least bring it up to him about your feelings. If he is truly your friend he will make an attempt to consider your feelings about this. If not, I would suggest you avoid putting yourself in a situation where you could be seriously hurt again.

I straight out tell them not to make promises to me unless they are gonna keep them. They state I will.. and I tell them if they do not keep them, that I do not want their promises they can keep them to themselves as they are already broken.. or I roll my eyes... and when they start talking about promises I walk off and no let them finish but I tend to be really brutally honest too - DNatureofDTrain

Do not leave that friends!

I don't know about punishment. I would sit your friend down and explain to him that your friendship has taken a step backwards due to lack of trust. I would describe how much it hurts when he makes promises and fails to keep them time and time again and that from now you will no longer take seriously whenever he says he is going to undertake anything. You may then need to distance yourself from him until he "gets it".