Here's the code:

truth coffin::Open(character* Opener)
{
  if(!Opener->IsPlayer())
    return false;


  if(!game::TruthQuestion(
	 CONST_S("Disturbing the dead might not be wise... Continue? [y/N]")))
    return false;
  truth Success = olterraincontainer::Open(Opener);
  if(Success)
  {
    game::DoEvilDeed(25);
    for(int c = 0; c < RAND_N(10); ++c)
    {
      v2 Pos = GetLevel()->GetRandomSquare();
      if(Pos != ERROR_V2)
	GenerateGhost(GetLevel()->GetLSquare(Pos));
    }
  }
  return Success;
}

DoEvilDeed seems to be called as soon as the player confirms that they want to open the coffin.

Opening the coffin in the Attnamese catacombs is an evil deed (25 alignment shift to chaotic) and will spawn up to 10 ghosts. Breaking the coffin spawns up to 9 ghosts.

(I think we investigated this a while ago? Anyway, confirmed while looking through code again)

Or at least as many times as you have applied nuts.
That should be easy enough to code too, just got to check if the player's nut counter is > 0 when you receive a groin scar.

Ascending stairs trains your leg strength. Descending them increases agility.
It trains your legs by 150 points, which is twice what you get from kicking things and (If I am reading the code right) takes less time.

Vomiting on Scabies' altar improves your relationship by 1.

Or... well we could make it so you can (a)pply nuts?

Oh, lemme clarify since it seems I missed a little something.

If your relationship with the god is less than 500, you have a 1 in 20 chance to improve your relationship with them and your WIS.
If your relationship is greater than 500 you have what I believe is a 1 in 2500 chance to spawn a friendly angel, train your WIS by a much higher amount and improve your relationship with the god.

There is a very small chance of spawning a friendly angel when you kneel at an altar (by sitting on it with _ )

Yeah, if you make him hostile by refusing to give him the shirt of the golden eagle the town will go back to normal once you defeat him.
If you attack him or otherwise piss off the town they won't stop once Petrus is down.

Petrus summons angels as long as he's hostile.

During my daily perusal of IVAN's documents, I discovered that there was in fact an idea for a liquid that would change the player's gender:

Material Ideas II.txt, line 17

cursed water of Nyanneechuan		changes the gender of a male player

And also some uh, other things:

testosterone				strength & beard growth
estrogen				breast growth