Lifetime of Silence, Behind the Green Door 

This is a military patch originating from the 504th flight test squadron, operating out of Groom Dry Lake, and Los Alamos AFB. Most of these projects are classified, and bearers of this patch are prohibited from discussing their occupation, hence, "A Lifetime of Silence". In a 1930's novel and a 1980's pornographic film, they both have green doors that a character cannot gain access to. In addition, the military, and most banks, use green vaults. So, the Green Door could be referencing that there are secrets that the public dosen't have access too. The true meaning of this patch is currently classified, and most likely will not be declassified in our lifetimes.

A lifetime of silence, behind the green door is the motto of the 504th Flight Test Squadron...

Lifetime of Silence, Behind the Green Door by AFC. Stanoff October 22, 2012

Facebook Silence 

Similar to radio silence but with facebook. The process by which you appear offline on facebook chat and check what others have written on your wall but do not reply or do anything that may appear in your news feed. This way, nobody else will know that you were on there.

Tim: Dude, I posted the funniest link on your wall and you never replied.
Mark: Oh yeah, I got that when Linda was really pissed off at me and I decided to go to facebook silence so she didn't know I was there.

Steve: I didn't go to the party last night so went to facebook silence so that people didn't know I sat in on facebook all night. This meant I could later give the charade of having had just as cool a night as the party-goers.

Dave: Dude, I haven't replied to that creepy girl who sits behind us in Chemistry on facebook...so now I have to stay at facebook silence whenever I log on so she doesn't know I'm ignoring her and just thinks I'm ignoring facebook.

Facebook Silence by Raving Professor No Legs September 6, 2009

Random acts of silence 

When something occurs that makes everybody stop talking and pay attention to the situation. Usually funny and very embarrassing. Can happen in a large group or a small intimate setting. Usually has something to do with racism.

Here is a perfect example of random acts of silence

Background noise from party

Becky: This party is awesome.
Ray: Yeah its alright. Its a little dark in here though, if you know what I mean?
Becky: I could ask him to turn the lights up.
Ray: I mean there are a lot of coons in here.

Record stops and everybody stops talking and looks

Random acts of silence by Cletus B Delicious July 25, 2011

awkward silence 

the silence in a conversation when all other parties feel that someone else should be talking, yet no one does. Usually happens directly after a weird comment is made or between two partners on a date.

After John made that dead baby joke, there was an awkward silence.

awkward silence by Confused Desi December 10, 2006

Blue Wall of Silence

The notion that despite police rules and regulations; a
police officer may not turn in or otherwise provide damaging information in regards to a fellow officer. The term is more for the use of only corrupt police officers and not the police force in general.

The Blue Wall of Silence is prevelant in many cases involving police corruption here in the State of Georgia.

Blue Wall of Silence by J. Malik November 20, 2005

Meat Silencer

The erection an officer of the law experiences as he is stacking up behind other officers before making a forced entry into a private dwelling.

Damn, Bob was grinding his meat silencer into my back just before we busted into that drug dealers house!!!

Meat Silencer by PrisonCityDub May 3, 2008

Radio silence

When someone dosen't return phone calls or text messages. Most commonly used when trying to develop a relationship with someone.

The girl seemed pretty into me when I met her at the bar, but when I called her the next day, I got total radio silence.

Radio silence by studio54 January 10, 2009