If you're looking for something colloquial, and which does not imply stupidity, "he offed himself" is the closest I can think of. It does not appear to refer specifically to suicide here and here (look only at the verb definitions), but others users may weigh in on whether it implies suicide or not.

An expression that gives me a not entirely healthy satisfaction and which I'll offer is:

He bit the dust.

It's a very old phrase that means "he died", but it just sounds so damn pathetic.

EDIT: This just occurred to me after seeing the f-bombs dropped in the comments. I remember that Tommy and Turkish in the movie "Snatch" use the expression

He got proper fucked

to refer to someone who's been killed. Actually, here they're referring to a rabbit, but the idea's the same. Urban Dictionary has a definition that doesn't do a whole lot of good, but it supports the idea that to be fucked could be bad, but to be proper fucked is terminal.

This term, to the best of my knowledge, is strictly British English.

A few creative options come to mind:

• He removed himself from the gene pool.
• He committed stupidcide.
• He died of jackassery. (This suggestion is a play on words off this TV show).

I feel like we can do better than this, but is this in the right direction?

Edit: OK, given what the OP has clarified, I add the following two:

• He gaped his maw.
• He fucked his skull.

These are not considered very well defined and are usually something you do to someone else, not to yourself, but it is definitely vulgar.

Okay... my suggestion may not be a "direct hit," but it might be in the right neighborhood.

I propose chlorinated the gene pool, or nominated himself for a Darwin Award.

• These terms are not exactly vulgar, but they might be considered rather edgy.

• They don't necessarily involve self-inflicted death, but they often do.

According to Wikipedia:

The Darwin Awards are a tongue-in-cheek honor .. [that] recognize individuals who have contributed to human evolution by self-selecting themselves out of the gene pool via death or sterilization due to their own (unnecessarily foolish) actions. The criterion for the awards states, "In the spirit of Charles Darwin, the Darwin Awards commemorate individuals who protect our gene pool by making the ultimate sacrifice of their own lives. Darwin Award winners eliminate themselves in an extraordinarily idiotic manner, thereby improving our species' chances of long-term survival."

Accidental self-sterilization also qualifies; however, the site notes: "Of necessity, the award is usually bestowed posthumously."

You can read about a few Darwin award nominees at this website. The expression "chlorinating the gene pool" is used as a subtitle for this Darwin Awards book.

EDIT:

When I first answered this question, I was under the (false) assumption that the O.P. was looking for a vulgar way to say that someone had taken his own life through some act of stupidity. It's since been clarified that's not the case.

Someone else has suggested bit the dust; I'll add bought the farm, which could perhaps only be considered mildly vulgar at best, but is used to describe when a person has met some untimely or ill-fated death, not necessarily through some fault of their own. TFD says:

buy the farm [Slang]: To die, especially suddenly or violently.

It's not as vulgar as some of the other suggestions, but I believe it has a rightful place in the conversation.