The former TOWIE star, who was evicted on Tuesday night, didn't hold back during an appearance on Bit On The Side after viewing a clip showing John telling Stephanie Davis to stop talking about Jeremy McConnell.
Gemma said: "That's the real Johnny. Look, I've lived in a house with him 24 hours a day. To be honest, he is a proper asshole. I had to get that off my chest.
"This is Gemma talking, this ain't GC. I think he's an asshole. I don't know what you're seeing but he would walk in a room and create an atmosphere, his face says it all. If he woke up in a mood it would bring the house down."
Fellow panellist Natasha Hamilton seemed to agree, saying: "I really wanted to like him but now I can't stand him and I hate the fact Jeremy isn't there, he's now picking on the vulnerable girl. He hasn't opened his mouth for weeks."
But panellist Mario Falcone disagreed: "I think he's done her a favour telling her, these last three days, just enjoy it and be yourself, don't go on about Jezza."
Stephanie had been up for eviction against Gemma and Danniella Westbrook and was absolutely stunned not to be sent home. Housemate Scotty T suggested it's because Jeremy was evicted on Friday, meaning Stephanie's had to mix more with the other housemates and viewers are seeing a different side to her.