Usher Pleads the 5th On Bieber's Racist Joke

6/3/2014 6:40 AM PDT

Usher On Justin Bieber's Racist Joke ... Pleads the 5th


had the opportunity to join the growing list of BFOJBs who have leaped to Justin Bieber's defense ... but instead he bolted.

Our photog spotted Ush yesterday in L.A. ... and of course asked about the video of 15-year-old Justin using the n-word as the punchline to a horribly unfunny joke.

You'd think, Usher -- being Bieber's longtime mentor and African-American -- would have something to say on the topic, but watch ... who knew he did a Houdini impression?

As we've reported, Floyd MayweatherSoulja Boy and others have already spoken up for Justin -- which makes Usher's reaction very interesting.