ATDM is short for arse to different mouth.
it is a variation for the more commonly used term "ATM".
which is arse to mouth in porno's.

Intelligence agency term for "psychological operation". A government or corporate-sponsored operation, usually taking the form of a "terrorist attack" or "crazed gunman on a spree", with the intent of panicking the public into demanding more police and laws inhibiting freedom. Psyops are usually carried out by drugging a civilian or group of civilians with aggression-promoting drugs, psyching them up, arming them, and sending them out to commit mayhem. Government-sponsored terrorism. See also blackshirts, conspiracy

Acronym, stands for Activate the Dick Machine. Typically necessary to shout when drunk and normal dick machine activation seems to be delayed.