Selena Gomez -- Did You Just Call Justin Bieber a D-bag?

Selena Gomez just appeared in a video dancing to the song "Everybody Knows (Your Boyfriend is a Douchebag)" ... which begs the obvious question ... is this a message directed at her ex-BF Justin Bieber?

Selena and her friends post videos like this all the time -- dancing to other people's songs -- but the timing of this one seems suspect, considering Bieber's recent wave of d-baggery.

It's possible Selena and her friends just like the tune ... and there's no hidden meaning ... but Justin and Selena have been known to communicate through song.

You'll recall JB sang "Cry Me a River" at a concert after they broke up. Selena later responded by performing the same song.

So we gotta ask ...