He's crazy dude.

I never wondered why he killed himself in the first place.

Uh there was a reason why the kid was in the institution, and Ratched knew how to set him off. She just couldn't take it that McMurphy had cured him of his lack of confidence and stutter so she had to knock him down by threatening to tell his mother.
"I really wish Gia and Claire had became Tanner" - Honeybeefine

Deep seeded feelings of Shame, Guilt and Anxiety have a power of their own and can make you do strange things knowingly or unknowingly.

Haven't you ever heard of "mother issues" before? Poor Billy was obviously brought up by a domineering mother, who happens to be best buddies with Ratched of all people, and probably instilled a strong sense of guilt in him from a very young age.

I suspect the mother was more abusively evil and a greater mental tormentor than Nurse Wretched

This scene shows Billy as a mentally ill person and Nurse Ratchett as a controlling, evil, manipulating, c-word. Notice Billy was not stuttering at all when he was talking with everyone about what he had done and then once Nurse Ratchett brings up Billy's mother, the stuttering rears it's ugly head.

that bitch probably just wanted something to hold over Billy's head. might not had any intentions on really telling his mom. but look what happened?
the bitch.

he left u NAKED in a DITCH!

It was pretty obvious that Billy had severe anxiety & emotional disturbance surrounding his relationship with his mother. The movie doesn't get into the specifics but it is enough to know he is very upset about his mother finding out & Ratched knows this & uses it to wind Billy up.
KZK

books are one thing, and the significant fundation for a film that stands very well for its own. No need to read the book to fill gaps which were obviously left open by the screenwriter and Forman. Because we do not know for sure its all up to speculation however the relationship between Billy and his "mother" really was. After all, both the characters of the novel as well as in the film are pure fictional, its up to everyone which illusion they are falling for.

Billy's mother is the core of his problems. The book spells it out a little better. She treats him like a young child to keep herself youthful in her own mind.
She would have really raked him over the coals if she found out, and he just couldn't take it.
Whoever suggested Ratchet was his mother, should reread the book.

It seems to me you didn't realize Billy had MENTAL problems.

http://viverdecinema.blogspot.com.br/

if that's true SnoozeALARM. u didn't lose ur virginity. u were RAPED! sorry to read this.

child please

I thought I was worldly, but this comment proves otherwise.

Well, the truth is that quite a few guys lost their virginity to my mother. So I was in good company.
Evacuation Com

Snooze alarm we have something in common, I lost my virginity to your mother too, but SHE was 21.
'Truth is like poetry. And most people beep hate poetry.

Is your mom Kay Parker?
Ephemeron.

Snooze Alarm, you lost your virginity to your mother? Are you serious? If so, you have my deepest sympathies and I can only hope you have transitioned to adulthood without too much pain.

I didn't want my mom to know when I lost my virginity. & I was 21. not contemplating suicide or anything, but I sure was upset & nervous at the possibility of her finding out.
I lost my virginity to my mother, so it's not like I could prevent her finding out.
If a private venture fails it's closed down. If a government venture fails it's expanded. M Friedman

Just watched it the other day after a couple of years and in my head two new theories emegered that would take Ratchets behaviour to a whole new level of insanity:
-she convinced Billy mother (given her manipulative skills) to send her son to her instiution and was working on that for years, maybe because she doesn't have children on her own or anyone in her life and sees him as a son who she can take care forever
-she actually IS Billy's mother and the "a mothers friend" thing is just used between them both to hide their relationship in front of the other inhabitants. It would also explain why she seems so personal attacked by him making out with Candy and sees it as a personal betrayal to his motherly love and a possibility of him leaving the institution and therefore her control for good.
What do you think of that?

I didn't want my mom to know when I lost my virginity. & I was 21. not contemplating suicide or anything, but I sure was upset & nervous at the possibility of her finding out.

you're going for, the last ride ah haaaaaaaa

It's sort of (heavily) implied that his mother is the center of his illness. Mentioning her name - since Ratched knows from therapy sessions how deeply disturbed his mother has left him - was the same as pulling a trigger.

Also he was guilty for ratting out McMurphy.

its set in 1963