The man with the dog must have just witnessed an altercation between George and Lynne, perhaps something along the line that George would be catching this evening's supper. Lynne kicked up a fuss and then proceeded to dive into the river. If this had not happened then this man with the dog has got some nerve to start a conversation with that question. It's up there with 'Your wife's a bit ugly' or 'You are pathetic in every way, shape and form.' Perhaps George was having a conversation with the man anyway when Lynne caused a stink. George then rolled his eyes causing the man to ask the question.
It just so happens that this man deals in the illegal trading and trafficking of women. He sees that he could get a lot of money out of Lynne and is willing to trade one of his uglier women for her. He would most likely ship her off to Amsterdam against her will, leaving George with an Eastern European lady who is just happy to sleep on a bed. George would no longer have to worry about his credit card or people looking at his wife. The man with the dog has gauged the situation and decided that George is the sort of man who he could do a deal with, and, if he isn't, won't take too much offence from his proposition.
George has decided against the deal. He believes that Lynne's breasts more than make up for the gifts he has to buy her. During all this time, Lynne has jumped in the river, had a small swim and got out again at the jetty. Saying that, it seems to be only her right hand that is dripping so she may just have put that in the water to check the temperature. After realising it was too cold, she kicked up another almighty fuss. It's no wonder it's cold. Not only is it the Thames but the outside temperature is low as George is wearing a polo neck and jacket. The only reason the man with the dog has his sweater tied around his waist is that he has just had a small run with his dog and has warmed up a bit. Lynne may be complaining but what does she expect. If she didn't spend all of George's money they could go on a more expensive holiday, if only her breasts would allow her.