As in, a man fully ejaculates semen, but his erection is still stiff and doesn’t go back to being flaccid/refractory period?
If so, is this a weird genetic thing or can somebody train themselves to do this? And if it’s genetic how common is it?
Yes
I think there is still some refractory period, but not enough for total loss of rigidity, and the younger you are the easier it is.
I’ve been training from I was in 3rd grade. In my late 30’s now and I’ve experienced it in the last 6 months, but anytime I do it now I think it could be my last. For the last few years the second time was hand assisted.
Yes…but it’s a superpower that degrades exponentially with age. Doggonit.
This pretty much… you don’t even have to “leave” the person your busy with, as it were. Also a less than ideal way to save money on condoms.
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Might not one of those “magic pills” help make such an achievement possible?
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Yup. I had that power at 18, but by 21 or so, it was already gone.
I was gong to post the power is called “being 18”. The term “hard as Chinese arithmetic” also comes to mind. Up until my late 20’s I could lay in bed and piss into the toilet 2 rooms away. Now I’m pushing 60 and the wife shoots further away when she cums than I do. Mother Nature is a sick bitch.
I know from personal experience that this is possible. Been awhile though, certainly not now in my 60s!
In fact, if you can keep your first orgasm somewhat quiet and keep on going, your partner will end up thinking you’re quite a stud. 
Happened once at the tender age of 27. Now, at 70, I would love to have the opportunity to attempt another tour de force. Volunteers?
You might not want to try this at home, kiddies. A prolonged, sustained erection, called “priapism” (Wikipedia page) can result in permanent damage to the penis, possibly leading to dysfunction later. Hows that for karma?
Certain drugs, legal and otherwise, can cause this.
My husband had this superpower when we met, when he was in his twenties. It did not survive his 30th birthday. I’m still holding on to my youthful superpower, which is imperviousness to hangovers, but I admit I haven’t been testing that one as vigorously as I used to.
Yup. I was able to do it in my teens/20s.
It was not common but it did happen on a few occasions.
Sadly, I have grown older and no longer can do that.
If you try to combine these two superpowers, you’re already lost when you’re still 18.
A guy goes to see a prostitute. They haggle over price for a while and finally agree on $300 for the service.
They go to a hotel room, the guy gets undressed and immediately starts whacking off.
The prostitute says, “Sweetheart you don’t need to do that.”
And they guy says, “What for $300, you think you’re going to get the easy one?”
My husband can still do it, at 54. He’s uncut; could that have something to do with it?
He can also have an orgasm by just lying there and concentrating.
As far as training to be able to do this goes, fully ejaculate is the key wording here.
It is possible to train to release a small amount of ejaculate (with less intense orgasm) and keep going with the same erection.
…I don’t get it. 
Alcohol won’t help with holding a long erection.
As others have said, it is completely possible but usually age dependent. I can’t do it now at 46 but I most certainly could in my twenties. Most people never believed me but I once had sex for 6 hours straight unaided by anything resulting in 8 plus orgasms with a single erection. I promise you that happened. I can still orgasm on demand with just a little notice and I can also delay them if my partner wants to. If you are young and have that superpower, enjoy it while you can.