Multiple photogs -- not ours -- were shooting Disick and baby Mason, when Scott turned to one snapper and said, "How close can you get?? ... stand back, you f**king idiot."

Seconds later, Disick snaps -- charging towards the photog screaming, "Don't get that f**king close to me!!!"

Moments later, Disick calms down and tries to explain himself ... saying, "I mean he's this f**king close to my kid man."