The kind of orgasm a guy has when his hands are tied out of the way and his penis is stimulated just until he can't stop anymore, and then let go. Neat to watch because of the way it bounces with each spurt. Embarrassing for the guy, especially if several girls are watching, and not real satisfying.
The most basic approach is to stroke his cock and then at the moment he first spurts you release his cock and let it twitch and spurt on its own. He will experience very brief pleasure at the first spurt but then once you release and there is no friction the orgasm becomes ruined and he is left frustrated. This is a good way to introduce him to the ruined orgasm.
Another technique is to release his cock before he starts to cum. This may take some practice because you have to anticipate when the orgasm is coming. If you spend a considerable amount of time teasing your guy or if he has been denied an orgasm for a long period of time, this becomes easier to do
Ruined orgasms are orgasms that are brought about as part of tease and denial play. A partner's genitals are stimulated to the very brink of orgasm and the stimulation is abruptly ceased. Often this will result in the frustrating experience of no orgasm occurring. However, if orgasm is inevitable and happens after stimulation has been removed, it will be much less intense and satisfying than a typical orgasm. That is why it is called a ruined orgasm.
Tease and denial play, including ruined orgasms, may be engaged in as part of a sexual relationship between a dominant and submissive partner. The dominant partner will control the submissive partner's pleasure and dictate whether they are permitted to orgasm. This can be employed as part or erotic submission or erotic feminization.