While all the participants chose numbers as low as 6 and as high as 9, Brett refused to rate his marriage at all and called the activity "trivializing," "so stupid" and dehumanizing. Brett argued his marriage was too complex to assign a value to it, and he rubbed his fellow grooms the wrong way.
Christina also didn't appreciate Brett's reaction, and she later warned Olivia to keep her eyes open because she was "seeing warning signs" in Brett that reminded her of her past relationships that didn't work out.
"Just the way he answers questions and how he... is so set. Sometimes you can bend and he just says all the right things. I've just dated guys like that before," Christina told Olivia in a recent Married at First Sight episode.
Christina then told the cameras Brett seemed like a "f-ckboy" and an "assh-le" and she didn't want Olivia to get hurt.
During Wednesday night's episode of Married at First Sight: Unfiltered, Olivia and Amani watched back a Season 11 clip of Christina and Olivia's tense conversation.
"I respect that she came to me with those red flags and concerns that she had, but I also have to figure him out for myself, because at the end of the day, I see the whole thing whereas she sees a few," Olivia explained.
Jamie pointed out it's difficult to form an opinion of someone when you've just met.
The host then asked Olivia, "Does Brett act differently behind closed doors when he's with you vs. the entire group?"
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"I think Brett definitely acts different," Olivia replied.
"When it's just Brett and I, I think he's a little more genuine and just a touch more real. I think when he's in a group setting, I feel like he lacks some confidence and maybe he tries to, like, one-up himself and kind of one-up everybody."
Olivia continued, "So I'm just really trying to figure out who he is -- which Brett is he? Because they're all a little different."
Jamie admitted, "That's gotta be really, really confusing."
Amani also wasn't fond of Brett after her husband, Woody Randall, informed her that Brett had ditched his fellow grooms at the bachelor party and did "an Irish goodbye," meaning he left the party without saying a word to anybody.
Given Amani had a similar impression of Brett early in the Married at First Sight experiment, Jamie asked Amani what she thought of Christina actually approaching Olivia and sharing her concerns about Brett.
"Do you think she overstepped her boundaries?" Jamie asked Amani.
"I don't think based on their relationship -- Christina and Olivia -- that she overstepped her boundaries," Amani said.
"I think if I felt as strongly as Christina with the red flags, I would have approached Olivia the same way."
Olivia went on to reveal how she planned to move forward with Brett after receiving Christina's warning.
"I think I still have to dive in 100 percent with Brett and still try to get to know him for who he is, and you know, just keep those concerns in the back of my mind and not forget about them," Olivia explained.
"And maybe if I see these behaviors, it'll start raising my own red flags."
Although they got off to a great start, Olivia and Brett really started butting heads once they returned to New Orleans from their honeymoon in Mexico.
Olivia hoped Brett would want to move into her house after the experiment, but Brett complained her place looked "sterile" and that "Barbie [had thrown] up" in the bathroom.
Given Brett owns his house, he hoped Olivia would want to move in with him -- but Olivia complained, "Walking through Brett's house, it's super messy and I'll be honest, his house in general is not that great."
Olivia said Brett's house felt like a "bachelor pad," and Brett admitted to the cameras it made him "feel like sh-t" when Olivia acted bored and unimpressed while walking through his home.
The pair also got into a disagreement over how to spend their money when Olivia makes significantly more money.
Olivia said she asked for a husband with whom to travel and enjoy dining experiences with as well as sporting events, but Brett is more focused on staying home to save for retirement and put money into his home.
Olivia and Brett began worrying they're not really compatible.