Mariah Carey -- Hey, Britney ... I'm Coming to Vegas ... Let's Party! (VIDEO)

Get ready for what could be the most epic girl's night out ever ... because Mariah Carey wants to party with Britney Spears.

Paps went bats**t crazy for Mimi as she left Craig's in West Hollywood ... just hours after we reported Mariah's deal to set up a residency at Caesars in Las Vegas was official.

While one might think Sin City is not big enough for both Mariah and Britney, Miss Carey told our photog she's totally down for a night on the town with Brit.

The Vegas gay bars will be hopping that night.