Nurse dancing is a minor tactic in NetHack. If you are naked and wielding nothing, a nurse will heal you instead of hurting you. If the healing attacks would heal you past your normal max hit points, your max hit points will increase. This is best done on a no-teleport level, such as the Castle or Sokoban, to prevent the nurse from teleporting away.
The Yet Another NetHack Frequently Answered Questions (YANFAQ) mentions that the ultimate nurse dance is to use a cursed scroll of genocide to create multiple nurses around you on a no-teleport level.
Details of a nurse's attack
The implementation of the nurse's attack is in line #1374 of mhitu.c.
If you are wielding a weapon or wearing any armor, the nurse will hit you for damage. Healers will not take damage; instead, the nurse will simply ask for your cooperation.
If you are unarmed and unarmored (quivered weapons, and worn rings, amulets, and blindfolds are okay), a nurse's attack will heal d7 HP, exercise strength with 1 in 3 probability, exercise constitution with separate 1 in 3 probability, and cure sickness of any type. There is also a chance that the nurse will raise your max HP by one.
There is only a one in seven chance for a given heal the nurse will even try to raise your max HP. In that case, you will always get an extra max HP if your current max HP is less than 5 * your experience level; above that, the chance of success gradually decreases until your max HP are 25 * your experience level, at which point no more max HP can be gained from nurses. If you are polymorphed, you will always gain a max HP when the nurse tries to give you one.
After each heal, there is a chance of something happening to the nurse. With one in 33 probability, the nurse will attempt to teleport away; if the level is no-teleport, she will become scared and flee for several turns instead. Furthermore, if the nurse tried to raise your max HP (successfully or not), there is a 1 in 13 chance she will simply vanish from the game world.
The best place to nurse dance is in a no-teleport level where dangerous monsters are rarely generated. Sokoban is usually the choice. Both variants of level 3 have an upstairs room which is relatively small and has one door that can be closed and locked, with Elbereth and a junk object in front. Note that monsters can be generated in the locked room as well, so also engrave Elbereth on the up stairs. Nurses ignore Elbereth, and most monsters generated in Sokoban respect it, but be wary of the various types of elves.
Note that monsters with wands can zap them at you from outside viewing range of Elbereth. If you have an amulet of reflection, consider wearing it instead of an amulet of life saving. Failing that, if your quest artifact provides magic resistance, acquire it before nurse dancing to protect yourself from wands of death. Elemental wands could still ruin your day, though.
If you have a pet, leave it on level 4 and visit it every 100 or so turns to prevent it from going feral.
The best (really, the only) way to generate nurses to dance with is by reading a cursed scroll of genocide. This will send in 4 to 6. Nurses are only randomly generated one at a time, and usually in areas fraught with danger. Atheists, be absolutely certain that the scroll is cursed, as a genocide cannot be undone. Reverse genocide does not violate the genocideless conduct.
If you can manage to avoid becoming permanently invisible, nurses will have an easier time finding you again after they stop fleeing. Unless you find an extrinsic source of invisibility early on, this is probably not worth forgoing the considerable advantages of being invisible. A mummy wrapping is useless for this purpose as nurses will not heal you while you are wearing one.
Once you are satisfied with your max HP, if you are non-human, or a Caveman, and have a tinning kit, consider killing the remaining nurses yourself instead of letting them poof. A blessed tin of nurse meat will restore you to full HP and can be eaten in one turn.