Russianspys little understanding of reality.

[Demonik1]

Obstruction of other players' vision. By creating something that's literally painful to look at you end up making it so that people can't look in that direction.

The only rule that talks about players vision is this.

Do not use PAC3 or E2 to obstruct player's movement or vision.

The cube is neither of these things, it's also doesn't hurt because it's just sitting in front of spawn, that's it.