a box is when 2 people touch knuckles (like fist to fist)as a personalized handshake or showing of respect or equivalence.
a mental box is when these 2 people want to do a box, but are to far away from each other.
while sitting in a classroom. person A on one side of the classroom and person B on the other side.
person A asks person B: how many points did u get on the test
Person B: 77
Person A: i got 80, mental box