According to Urban Dictionary:

The Blackpill is basically the ultimative and hardest to swallow Redpill.

It is about realizing nothing matters and there is nothing you can do that will change anything, it depraves you of all positive thought and makes you want to get some sort of meaning out of this limited time we have.

Basically extreme nihilism. That's why its not a called a red pill, since beyond that. "John took the blackpill recently. He is depressed since that..." "Tell him to just take the Bluepill then" "Impossible. once you go black you'll never go back"

I reckon @SilentJohn@kbin.social realised they were not going to be Kaz, got depressed then put on (bad) weight.