Drake just dissed Kid Cudi by making fun of his life-threatening depression ... and people are pissed.
Drizzy dropped new music on the eve of his 30th birthday, and one of the songs -- "Two Birds, One Stone" -- clearly calls out Cudi as an angry guy who takes drugs to deal with reality.
You'll recall ... Cudi called out Drake and Kanye last month for refusing to work with him. He checked into rehab a few weeks later for depression.
Apparently turning 30 brings out Drake's worst behavior.