It's basically ending a sentence with a comma and "Bitch!", as a way of someone verbally making an exclamation point in dialog. It did get overused, so now it's a Discredited Trope. You're as likely as not to see it thrown in a sentence just to be funny, even though there is no other reason to emphasize a point this way. This can overlap with Quote Swear Unquote, Obligatory Swearing. Compare (but would not overlap with) Verbal Tic, Precision F-Strike. Examples of This Is for Emphasis, Bitch include: