Why does toast land butter-side down?

Answer: Table height and rotation physics

Table height and rotation physics ✓ — Correct! Toast slides off the edge of a table, tips, and starts to rotate as it falls. From an ordinary table about 75 cm high, a slice of typical size tipping at typical speed has time for roughly half a turn before it hits the floor, so the buttered side, which started on top, is usually facing down. Physicist Robert Matthews worked this through in 1995: the outcome depends on table height, slice size and how fast it leaves the edge, and for a full turn, which would bring the butter back on top, the table would need to be nearly three metres high.

Murphy's Law in action — It feels like Murphy's Law, but the butter-down landing is a matter of geometry: an ordinary table gives a tipping slice about half a turn, which is why it happens more often than not, not because the universe is against you.

Static electricity attracts butter — Butter is not noticeably charged, and static electricity plays no part. The slice's orientation on landing is set by how far it rotates during the fall, which depends on the table height and how it tipped, not on any attraction between butter and floor.