go off the deep end

Related to go off the deep end: take a back seat, without a hitch, along the lines

go off the deep end

1. Literally, to jump into the deep end of a pool (as opposed to the shallow end). Don't let Sally go off the deep end—she doesn’t know how to swim.
2. slang To become crazy or irrational. A; "Now your father thinks the neighbors are plotting against him." B: "Wow, he's really gone off the deep end!" Whoa, man, stop yelling! I only put a tiny scratch on your car, so there's no need to go off the deep end.
See also: deep, end, go, off
Farlex Dictionary of Idioms.

go off the deep end

 and jump off the deep end 
1. Lit. to jump into a swimming pool where the water is over one's head and one needs to be able to swim You are still only learning to swim. Are you ready to go off the deep end? He jumped off the deep end where he would make a bigger splash.
2. Fig. to become deeply involved (with someone or something) before one is ready. (Applies especially to falling in love.) Look at the way Bill is looking at Sally. I think he's about to go off the deep end.
3. Fig. to act irrationally, following one's emotions or fantasies. Now, John, I know you really want to go to Australia, but don't go jumping off the deep end. It isn't all perfect there.
See also: deep, end, go, off
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

go off the deep end

1. Become unduly excited, overwrought, or angry. For example, When he heard about John's smashing into his car, he went off the deep end. [c. 1920] Also see in deep, def. 2.
2. Be irrationally carried away, act irresponsibly or heedlessly. For example, Just because you like her looks doesn't mean you should go off the deep end and propose. [c. 1920] In both of these colloquial usages deep end alludes to the deep end of a swimming pool.
See also: deep, end, go, off
The American Heritage® Dictionary of Idioms by Christine Ammer.

go off the deep end

mainly AMERICAN
1. If someone goes off the deep end, they start to behave in a crazy or very extreme way. Ray gives a chilling performance as the seemingly nice cop who goes off the deep end and starts terrorising a couple. At first they thought that I'd gone off the deep end and had lost my mind.
2. If someone goes off the deep end, they become very angry. My dad went off the deep end when he found out what I'd done. Note: The deep end is the end of a swimming pool where the water is deepest.
See also: deep, end, go, off
Collins COBUILD Idioms Dictionary, 3rd ed.

go off (or go in off) the deep end

give way immediately to anger or emotion. informal
This expression refers to the deep end of a swimming pool, where the diving board is located. In the USA the phrase has also developed the meaning ‘go mad’, but in either sense the underlying idea is of a sudden explosive loss of self-control.
See also: deep, end, go, off
Farlex Partner Idioms Dictionary

go off the ˈdeep end

(informal) suddenly become very angry or emotional: Don’t tell your father that you lost the money — he’ll just go off the deep end.
See also: deep, end, go, off
Farlex Partner Idioms Dictionary

go off the deep end

in. to do or experience something in the extreme: to fall madly in love, to go crazy, to commit suicide, to fly into a rage, etc. I saw what he had done, and I just went off the deep end. I was in a blind rage and didn’t know what I was doing.
See also: deep, end, go, off
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • jump off the deep end
  • in at the deep end
  • thrown
  • deep sleep
  • cork high and bottle deep
  • hold (one's) breath
  • hold breath
  • hold one's breath
  • hold your breath
  • beyond (one's) depth
References in periodicals archive
"Karrueche doesn't think Chris is about to go off the deep end. This was an isolated situation that never would have happened if people kept their unnecessary comments to themselves," a source told (http://hollywoodlife.com/2014/11/04/karrueche-tran-chris-brown-anger-adrienne-bailon-attack/) Hollywoodlife.
"Every night my wife phones to see what time I'll be back and then goes running round the house clearing things away so I won't go off the deep end.
Unfortunately, Ryan puts a spanner in the works, prompting Steve to go off the deep end. The Rovers landlord later confides in Lloyd that he never expected a romance with Michelle to include so much baggage.
The supposedly parallel developments of film's three main strands never meaningfully connect--Neely and Tonio are reconciled well before he's arrested, the two move to another apartment before their ex-neighbor has a chance to go off the deep end, and no one seems to give a damn who killed the diva.
You can feel sympathy for Whately when, interviewed by the police over the ODed death of his smackhead partner, he's required to say things like "I'm a doctor for God's sake" but you should also be grateful for Gannon slipping in the line "my work and family keep me going" just so you know he's probably going to go off the deep end when both come under threat.
While the Arabic network has come under fire for perceived anti-American bias in some of its reporting from time to time, Beck appeared to go off the deep end Thursday night.
Others, like your husband, go off the deep end and their coping strategy is to change everything.
He gave me another look and for a horrible second I thought he was going to go off the deep end again.