What's "can you believe this guy" mean? I feel like "can you believe it" would be better. What's she trying to say?

Native speaker’s answer
Rebecca
The difference with adding "this guy/girl/etc." to "can you believe it" is that it places emphasis on the actions of the person being mentioned. They have pretty much the same meaning, but "can you believe it" is used more often to refer to a situation, and "can you believe this X" is more used to refer to the actions of a person. In either case, it's an expression used to express surprise. Ex: I aced the test! Can you believe it? Ex: Can you believe this guy? He just bumped into me without saying sorry.