Does anyone ever get on the PA and say something like "hey guys we have some leftover pizza in the armory if anybody wants some" and then there's a mad shuffle to the armory enough so that the boat starts to lean a little bit and when everyone gets there there's some mother rough rider smiling with pizza crumbs all over his face and a big JK LOL sign?
Groups of guys moving around the boat can definitely affect the trim. It's one of the things folks like to do for newly qualified Dive Officers. One of the things that we always will do every watch is to get a perfect trim (the boat is neutrally buoyant with zero angle on the ship) at 3 knots (which is very slow). We do this to make sure if we have to go to periscope depth in a hurry, we have a reasonably good idea of the trim so the Dive knows how much water to bring on. This ensures the boat doesn't accidentally broach in places that aren't welcoming to a nuclear sub in their midst...
So, while newly qualified Dives are trying to do this, some of their "buddies" will go to the front end of the boat and wait. The Dive sees the front end is heavy, so pumps water aft. While that's going on, the guys all move aft. Now, the boat is heavy aft and the Dive has to pump fwd. Rinse and repeat.
These are the types of hilarious hi jinks you come up with on Day 70 of a patrol...