Dwight Howard -- Great at Dunking, Just Turrible at Impressions

Dwight Howard's working on a backup plan if this Lakers thing doesn't work out -- celebrity impressions ... and he busted out his Charles Barkley today in Beverly Hills.

The Lake Show's new all-star was leaving a salon in the 90210 (he really likes BH), and when someone asked him to whip out his Barkley ... Dwight jumped right into it.

We'll say this ... it's okay. Not as good as the Kobe Bryant impersonation he did last week, but decent.