I can imagine a 125+ gallon tank working fine... the reason that a 10 gallon wouldn't work is because the fighting males wouldn't be able to flee far enough, spending time miserable because of stress. 125 gallons, though, is plenty of space to lose a pursuer and de-stress. Females can flee males, males can flee females, males can flee males, and females can flee females. The amount of space is key. And 125 gallons is a LOT of space, lol. So I wouldn't say that males can NEVER be placed together, but you MUST, MUST, MUST have a large, heavily planted tank with multiple hiding spots.
But to answer the question, as the others have said, no, you cannot place two males in a undivided 10 gallon tank. It would pretty much assure death. Don't believe youtube.