Why did he say "who is this guy" instead of "who is he"? Is there any nuance difference? When can I use "guy"?
Yes, when he says "who is this guy" here, there is a slightly different meaning than if he were to have said, "who is he". "This guy" implies that he is not excited about meeting him and he doesn't want to get to know him. The phrase "this guy" can be used to refer to someone who is intruding or being rude, although it can also depend on the tone of voice and where the stress is placed on the words by the speaker. Here's a few examples of where "this guy" might have a negative connotation: Ex: Who does this guy think he is? Ex: This guy just cut me in line. However, the word "guy" doesn't always have a negative connotation. It can be used to simply refer to a man or a group of people. Ex: Yesterday this guy complemented my car. Ex: What are you guys doing today?