Justin Bieber -- Jesus Christ, Flo Rida's Got a HUGE ...

SIZE MATTERS ... and at last night's Heat-Pacers game, Justin Bieber was in the teeny weenie Jesus department compared to Flo Rida.

Justin dropped by the American Airlines Arena for Game 7 of the Eastern Conference finals, wearing his bandwagon baseball cap and Hefty-brand button down ... but the tiny Jesus really made a messiah of his outfit.

Flo Rida vs. Justin Bieber -- it's a slam dunk, right?