Why do people say the boyfriend instead of my boyfriend?

Why do people sometimes say the boyfriend instead of my boyfriend? Is it slang native to a particular part of the country?

Most commonly I hear it used by people who generally say "my boyfriend" ("My boyfriend is from Chicago") but might say "the boyfriend" when they find themselves saying something stereotypically what someone would say about a boyfriend, e.g., "I got my hair cut today, hope the boyfriend likes it!" or "I think we're free on Friday, but I'll have to check with the boyfriend!"

I'm assuming you mean something comparable to "out with the wife," etc.

In that case, I think it just boils down to tradition and culture, and the memetic nature of the evolution of language. It also depends on the emotion that the speaking individual is wishing to communicate.