Ronda Rousey Marine Concerned After BF Revelation ... 'Hope She Doesn't Back Out'

A wise Batman villain once said, "Never rub another man's rhubarb" -- which is why the marine who asked out Ronda Rousey is concerned that their date to his Marine Corps Ball could be called off.

As we previously reported, Lance Cpl. Jarrod Haschert asked Rousey to his Marine Corps Ball earlier this summer in a video that went viral -- but to his surprise, she accepted the offer.

But that was before UFC fighter Travis Browne went public about his relationship with Rousey -- declaring on Monday, "She's my woman and I am her man."

So, we hit up Haschert about the news that Ronda's spoken for -- to which he simply replied, "Damn. I really hope she doesn't back out."

BTW, Haschert is such a gentleman, that when we jokingly asked if he'd consider fighting Browne over Ronda, he told us, "That would be a tough fight! She's a great woman with an amazing personality. I'm sure he's a great guy."

The ball is set to go down in December -- stay tuned.