This guy. This thing is the exception of all exceptions when it comes to NMBs. It is a naturally occuring alkaloid in plants of the genus Erythrina. The plants themselves are beautiful with red flowers and are sometimes called coral trees. And you can BUY them! You can just get a dihydro-beta-erythroidine plant if you live in the right place, usually the southern US, where the plant grows. But be careful, because in order to get a plant, you have to only be doing it for "ornamental purposes," not for the fact that it's poisonous. So basically, pretend you have no idea that it's poisonous and just tell whoever's selling it that you think it looks pretty and boom, you've got yourself a deadly NMB!
What's so strange about this NMB is that is has NO quaternary ammonium. It has no N+ at all, but it is still a potent NMB. It gets even better - if you actually make the nitrogen in it quaternary, it becomes less potent. Weird stuff. It can also kill you if you eat it. NMBs are generally safe to eat unless you have cuts in your mouth or something. But not this one. Since it doesn't have the positively charged N+ that the others do, it is not as polar and can pass through your digestive tract linings into your bloodstream where it is free to wreak havoc in all the muscles it travels to. I have not eaten DBE, but it most likely tastes bitter, since it's an alkaloid. However, you have most likely eaten a plant from its family. It is in the plant family Fabaceae, which happens to be the same family as green beans and peas :)
The reason it's not used in medicine is because it causes hypotension. It's the same reason malouetine (origin of steroid structured NMBs) was never really used itself even though its derivatives are hugely popular today.