Isaac doesn't think Siavash poses any threat to his relationship with Noirin, but admits he wishes the pair had not kissed.
Isaac has called Siavash a "f**k from 'Pirates Of The Caribbean'."
The 'Big Brother' newcomer took a swing at the long-haired party-planner before entering the house, and admitted he was upset his ex-girlfriend Noirin had kissed him.
American musician Isaac, who was living in Ohio before coming on the show, said: "I come over here on a 24-hour flight to reconnect with an ex-girlfriend. And the one and only 'Big Brother' episode I have ever seen in my entire life is her sucking face with some f*** from 'Pirates of the Caribbean'."
Isaac - who locked lips with Noirin shortly after entering the house this week - added he was not too bothered about Siavash, insisting Noirin would always pick him over the flamboyant Iranian.
He said: "I don't even know this Siavash dude. I don't know if he's a good guy, bad guy, a creeper. He could be an amazing guy. Do I think he's competition? No.
"I just gotta roll up there and let her know 'daddy's home'."
Meanwhile Siavash revealed his discomfort with the new couple in the Diary Room.
He told Big Brother: "I'm trying to force myself to dislike the guy, but I haven't talked to him at all. I don't know what kind of person he is, so I have no reason to dislike him.
"I want to talk to him, but what do I say? There's nothing to say."