How common is simultaneous orgasm? a friend insists on having this in his romantic relationship. i said this is exceedingly rare and unrealistic.

Difficult to say: Not a lot of research out there on the topic. From couples work, i can say that it is less common in couples than non-simultaneous orgasm. Couples can try to arrive at the same destination with some practice (which could be fun :)), but you still may have more random results in this experiment.

No data available: It can happen, but it is not necessarily a desired or possible goal for many couples.To insist upon it would be foolish and disappointing at best. It places undue strain on the timing of orgasm and could lead to excessive performance anxiety and eventual performance failure if it were demanded in a relationship. I think your view is the correct one.