Reddit

r/Art is on the John Oliver train as well, just in an artistic form.

Explainlikeimfive should mostly be "you'll learn about it when you're older".
Space should be pictures of empty rooms or walls.
AdviceAnimals should be random bits of advice one animal would give to another, like "see how that hole in the wall looks weird? That's a window. Don't fly into that."
AbsoluteUnits? Just pictures of items that have units marked on them, like a 20kg bag of mulch or 5L of water.