Analysis.

(Remember: this analysis is particularly true about British language and culture, though mostly it is the same for other English-speaking countries like Australia and the United States.)

Sentence by Sentence analysis.

Sally: "Well, Ivan. I hate to say I told you so, but it looks as though one of your investments has run into problems."
("I hate to say I told you so" is a polite way of saying "I told you so".)

Ivan: "Oh no. It all seemed to be going so well. Which investment were you talking about?"
(Ivan thinks he knows what this is about, but he wants to check.)

Sally: "Have you seen this article about Wagnerox?"

Ivan: "Yes, they have gone bankrupt. It's a pity. They had some really clever technology that might have changed the way that you use computers. But their business plan was not up to much, it turned out."
(Ivan is not really answering Sally, who already knows this. She wants to know about Ivan's investment in Wagnarox.)

Sally: "Peter was telling me that you made a big investment in Wagnerox last week, while I was out of the office."
("While I was out of the office" is an accusation. Sally knows that Ivan did this deliberately.)

Ivan: "Well, not that big an investment. I went in for twenty thousand pounds actually."
(This is in fact a large amount to lose. Ivan is not answering the accusation either.)

Sally: "Why didn't you tell me?"
(Sally is getting angry, and she makes a direct attack.)

Ivan: "I thought I'd leave it to Peter. He seems pretty efficient. And I knew you wouldn't be happy."
(This accuses Peter of always running to Sally with bad news. Ivan now admits that he knew Sally would try to stop his deal.)

Sally: "Can you blame me? We have to explain to Mr Blake that we have lost £20 000!"
(Sally is very upset. She thinks Ivan has lost a lot of money, and is being stupidly cool about it.)

Ivan: "Why? What have you done?"
(Ivan knows what Sally thinks. But he knows that he has not lost any money, so he pretends that he thinks that since Sally has said "we" it must be her.)

Sally: "Don't be silly, Ivan. I'm talking about Wagnerox. Haven't you read the article? The shares are worthless."
(If Sally was less agitated she would now start to wonder if Ivan was not playing some sort of game.)

Ivan: "So I will have no trouble buying the shares back then, will I?"
(Ivan has had his fun, and now he decides to tell Sally what is going on.)

Sally: "What do you mean ?... you mean ..?"
(Sally is now working out what has happened.)

Ivan: "Yes, Sally, I shorted them. That means, Sally, that you sell shares you don't have. Last week I sold £20 000 worth of Wagnerox shares. Now I have to buy them to balance my position. The shares are still trading at 0.25p. So I am going to make well over £19 000 pounds."
(The explanation is very detailed, because Ivan is being patronising. (This is also why he repeats "Sally" twice.) Ivan is treating Sally as though she knows nothing about share dealing. This is his revenge on Sally for accusing him of losing money and listening to Peter's stories.)

Sally: "Ivan, you are a beast."
(Sally calls Ivan a "beast" because she knows that Ivan knew all the time that she was wrong, but he let her get upset without telling her the truth.)

Ivan: "I'm a beast who has just done a nice bit of business. Do you fancy a drink after work to celebrate?"
(Ivan does not deny the accusation. He suggests a drink to show that he was teasing her in a friendly way. He also indirectly suggests that Sally can have a drink with him to make up for not having trusted him.)