[yareally]

Sometimes I will use it in a conversation when referring to a third party unknown to the person I am talking to and the subject's gender has no bearing (like in my first comment).

For example, "Oh, I know a guy that knows X," "I know a guy that is a fan of X" or in a less positive manner "That guy just cut me off [on the freeway]!" (since you rarely see who it might be and their gender doesn't matter)

I could say "dude" as well, but sometimes dude might be too informal. I could reword it with a number of other pronouns, but it depends on context and whom one is talking to.