50 Cent -- Bodyguarding for Carmelo ... Terrifies TMZ Photog

This clip is pretty damn hilarious -- 50 Cent doing some bodyguard work for Carmelo Anthony on the streets of NYC this weekend ... and scaring the living hell out of our TMZ photog.

We were trying to ask Melo about the Ray Rice situation -- when 50 jumped in.

Of course, the two superstars are good friends and business partners ... currently out promoting their new SMS Audio headphones.

But if that doesn't work out, 50's probably got a career in personal protection.