Motto of the Wild Weasels - You Gotta Be Shittin Me
The expression comes from an elite group of fighter pilots that were formed in the Vietnam war in 1966 to combat increasing losses from Soviet SAM (Surface-to-Air) missles. The mission of the Wild Weasel was to to fly ("troll") ahead of incomming F-105 Thunderchief formations. In essence, the mission was to trick the VC (bad guys) into thinking that the WW (Wild Weasel) was an attaching Thud, when they targeted the Weasels, they would initiate a tactical manuver to hit the SAM site with a radiation seeking missle.
The term YGBSM comes from one of the original briefings when a weasel pilot stated, in content "You're telling me that I have to fly downtown Hanoi, with one bullet, and I can't shoot at him until he shoots at me..... you gotta be shitting me" --- YGBSM

In memory of the Weasels -- my beloved father Lt. Col Larry W. Biediger (KIA) , his weapons officer, Claude Silva (KIA), and Col. David Everson (USAF RET)

A phrase to describe someone who is cognitively degenerating. Synonym of "going off the deep end". Can have varying degrees of severity.

Reference to the song "Hey You" by Pink Floyd. The line "and the worms ate into his brain" makes no sense in an otherwise linear and literal narration throughout the lyrics.

During the Viet Nam war, US pilots were getting shot down because of surface to air missile SAM sites. In an effort to counter-act the losses, the USAF came up with a tactic called the hunter-killer team concept. This tactic required a pilot, the hunter, to fly low over an area of suspected SAM sites in order for the sites to start shooting. Once the SAMs started shooting, pilots in follow-on aircraft, the killers, dropped bombs and fired missiles to disable the SAM site. When told of the new tactic at a pre-brief, one pilot was reported to respond, "You've gotta be shittin' me!" The term is associated with Wild Weasel pilots who flew F-105s, F-4Gs, and currently F-16s.
Currently, the term is used as an exclamation of shock or disbelief.

you gotta be shittin me