How to perform:

open a door and stand on the part of the block the door will be on when closed, then crouch (make sure to have no items in your hand)and stay crouching until you close the door, when closing the door, you will be standing inside of it, and if you try to move around (while still remaining in the door) you will move a little bit faster.

if you perform this glitch (even with crouch set to toggle) you will appear to be standing in the door but your hitbox and sightline white still remain in the crouching state until you leave the door,