I have said, time and again, a ruined orgasm is a joy to behold. But I still get questions concerning how it is done, what it looks like, and how to know if it was ruined or not. So, let's start at the beginning...
Your first indication that your partner's orgasm was ruined will be the disappointment he exhibits. He may strain and try his best to make it feel like a real orgasm, but he will fail. His ejaculate will simply dribble out (as in the photo on the right) and he will not feel the usual thrust he gets on that that first “blast” or two. Instead, though try as he may, he will not get that satisfying feeling he is used to. On the upside, because he has not been satisfied, he will not want to stop.
At this point, since he is still aroused, he will be willing to do just about anything for you in order to achieve that satisfied feeling. He will be willing to do things that, normally after an orgasm, he would not want to do. You see, since he has not been sexually satisfied, he will still feel all the same urges he felt BEFORE the ruined orgasm. So now would be a good time to have him lick up, or drink his ejaculate. After all, he is still sexually excited and wants you to give him another chance.
The key to ruining any orgasm is to stop all stimulation at the last possible moment. Don't be afraid to experiment with this. It may take you several tries to get it right. But if you stop too soon, you have not lost anything, you have only managed to edge him. He will enjoy that, too. Give him a chance rest, maybe twenty seconds or so, and start again. It's the build up that gives him the most pleasure, so don't be afraid to make it last as long as you like.
The idea is for the both of you to have fun with it. If it becomes a chore for you, then you need to look for new and different ways of teasing his penis in order to reach the desired level of arousal. Try to come up with something new every time you do it. After all, variety is the spice of kink.