This trick allows you to clip through walls and slopes using a decent amount of lag. Quickly throw up to four oranges in first-person mode. As the game lags, you might be able to clip through the wall with certain moves. Depending on how much the game lags as you touch the wall, you'll end up out of bounds.
It works on virtually any wall, but its consistency and difficulty varies by the wall you're trying to clip through. Make sure to get as much lag as you can by changing your camera angle and having it show more textures. Even if your setup is perfect, a lot of luck seems to involved because lag is the least reliable factor in this game. However, the consistency can also be optimized by timing the appropriate "clipping move" perfectly so you get to the wall right as the lag spike kicks in.
With DK, do a kick and turn away from the wall so you'll face the opposite direction and move backwards into the wall during the lag spike. With Diddy, try doing a Chimpy Charge straight into the wall. With any other kong, you can try doing a long jump. This is significantly harder, even in areas that have a lot of lag. However, some areas are even laggy enough to simply walk through a wall after throwing oranges.
Damage Boost Method
In some places a damage boost allows you to clip through the wall. Combined with the lag when quickthrowing up to 4 oranges, you will be even more likely to clip.
Aztec Lobby Early
Make sure you have at least one slice of melon left. Get into one of the corners by the door to the Aztec lobby. You might want to walk up to the middle, turn around, jump backwards and Simian Slam in the corner to get closer to the wall. Take out your camera and line up your angle the way you prefer for this trick (there are several setups but none of them is 100% consistent). When you're done, put the camera away and throw some oranges. Depending on your angle setup, you will need a different amount of oranges. There are setups that allow you to clip with just one orange, but these are pixel-perfect. You will usually want to throw four oranges to maximize your chances of success. Also try thinking of a quickthrow pattern you might use (don't just throw them all as fast as possible, instead e.g. chuck one orange, wait a split-second and then throw three more oranges). Essentially, the best way of getting this trick to work is finding out your own way of setting up your angle and quickthrowing oranges.
Make sure you have at least 2 melon slices left. Kill the enemies in the starting area of Factory. Walk toward Snide's H.Q. and up into the left corner. Walk just a small step to the right (so you're still on the left side of the leftmost line on the ground) and turn around while holding Z. Take out your camera, line up your angle correctly and quickly throw four oranges. The oranges should all blow up at once and throw you behind the wall.
From there, hold Z and turn around so you're facing the exact opposite direction from where you came from. Walk straight ahead or do long jumps until you fall into the room where Chunky is trapped. If you get lost, you can also orient yourself with the star from the tag barrel nearby.