I can't give you a figure because I have only been with my husband for the past two+ decades and before that, with one other. But it occasionally happens to them all (once or twice a year, and it's nearly always from fatigue or stress or illness) and I'd guess that one-night-stands might have a higher rate of problems than commited relationships because the performance pressure is greater and the possibility of alcohol- or drug-aggravated erection problems is also higher. Just a hunch. Most grownup guys with any sense know better than to talk a big game till after they've delivered the goods, if you know what I mean.