Justin Bieber Spitting Again -- Caught in the Act

Here it is ... hard proof Justin Bieber is a revolting, germ-spreading spitter.

The photos were snapped Thursday in Toronto, where Bieber was perched atop his hotel balcony. We can't tell what, or who, was directly under him as he dropped his saliva-bomb.

It is worth noting ... hordes of fans were gathered outside the window of his hotel room all day -- he even posted a Bieberview pic on Instagram.

Also relevant ... multiple people have accused Bieber of using spit as a weapon -- including some woman at a gym, his neighbor, and most recently ... a nightclub DJ.