Shady Irish Sneakout (verb) is the act of leaving a social gathering without telling anyone goodbye. There can be various reasons for such behavior. Sometimes, (1)the person leaving without providing a salutation simply wanted to leave without having to say "good bye" to all of his/her friends. In other cases, (2)the person committing the Shady Irish Sneakout may have wanted to avoid saying "bye" because of the worry the others would try to convince him/her to stay. The Shady Irish Sneakout is also common when (3)someone has had too much to drink and have simply determined that they need to leave immediately.
ORIGINATION: 2001 - After a concert at La Zona Rosa in Austin, TX, a group of friends were at the adjacent Backstage Bar when they noticed that Bob Madden had suddenly left unannounced. Upon noticing this, Kevin Brelsford said “He did the Shady Irish Sneakout.” Bob is of course a huge Notre Dame fan and alum and has the Notre Dame Leprechaun tattooed on his arm, thus the “Irish” reference. The likely reason for the Shady Irish Sneakout was a combination of reasons #2 and #3 above.
You are with a group of friends at a party, bar, etc. and all of a sudden notice one of your friends has unexpectedly left. "Where did Bob go?" "He must have done the Shady Irish Sneakout".