Wasn't I already being pedantic enough about "Or peeling two stickers off a corner piece and swapping them to change the parity and make it impossible to solve."?
If you really want to make it physically impossible to solve and frustrating, swap two stickers between two cubes so they both have the wrong number of two colors, especially annoying with two colors on different faces of the same piece.
If you really want to make it physically impossible to solve and frustrating, swap two stickers between two cubes so they both have the wrong number of two colors, especially annoying with two colors on different faces of the same piece.