The act of collecting large amounts of saliva on your index finger and then sticking it in someone's armpit with a twisting motion. Usually done from behind to allow for the element of surprise and to give you a chance to run.
Index fingers from both hands can be used at the same time for a double-barreled soggy molly.
While Billy-Bob was giving the nerd a wet willy, Jimbo was giving him a soggy molly.