A tense chat between the two sort-of love birds occurred in the kitchen with Christopher having had enough of being treated like a child by the rest of the house.
He complained: "It feels patronising, sometimes in here I feel like I'm treated like a child.
"I am an adult, I've lived by myself by five years, I can took after myself and care for myself, I don't want to be treated like an ignoramus."
He added: "It drives me up the wall, it drives me up the wall, I just feel like a child."
But Mark insisted he was only looking out for his pals, replying: "You'll thank me for it."
Christopher it back: "No, I won't."
He went on: "I know I'm an intelligent person, I know I'm not stupid but I don't like to be treated like I'm stupid."
Christopher concluded: "You don't know me at all, you really have no idea about me at all and what I'm capable of.
"Please don't underestimate me."
In last night's show, new housemate Zoe quizzed Christopher and Mark on their relationship and asked when it started.
Mark told her: "Since Matthew went."
He went on to say that if Matthew hadn’t been evicted he probably wouldn’t have become as close to Christopher as he has.
Big Brother 2014 airs tonight at 9PM on Channel 5.