I've said it since the start.
Marcus is a nice decent bloke, but a BLOKE! He is insecure, brash, a show off and over confident, but it's mainly a mask. Especially when his feelings are concerned. He has DEFINITELY been hurt badly before, hence why he throws up this massive shield to protect himself. I think if he had cried over Noirin he may have gained more support and sympathy.
He has a good heart and he is one of the most observant and insightful housemates they have ever had in there. He just ruins his good work by being completely the opposite when it comes to himself and how others percieve him, hence all the Noirin business. His vulgarity amuses me and certainly doesn't offend me and all his anti BB stuff and rule breaking is absolutely hilarious to me, but I can see why others don't like it. He has a great sense of humour and imho would be a very good and loyal friend. All in all there are far worse in the house and certainly far nastier, especially Lisa and her twat of a stenchman David, whose mask has slipped so far in recent days, it is now stuck around his giant duck shaped arse. Mind you, how it got over his Shrek like head is beyond me.
**edit**
BTW I am not saying he is perfect, far from it, I just think he is often misunderstood and not to everyones tastes.