Hilary Duff -- Paparazzo Goes Down ... HARD!

EVERYBODY loves watching people fall down ... even Hilary Duff ... who couldn't help but smile last night when a paparazzo lost his footing and ate it HARD ... and it was all caught on tape.

Duff was leaving Aventine in Hollywood when an overzealous and underbalanced photog tried to get in position for a shot ... and wound up flat on his back.

You gotta see Hilary's post-fall commentary, which included gems like ... "exciting" and "pretty awesome."