Is the term "half-assed", the term to describe something done without the appropriate care, just a malapropism of "haphazard"?

No – I don’t think so. I think it evolved separately. Although I don’t really know why we would say something was done in a “full-assed” way.

It might be. That is one theory of the phrase’s origin. “half-assed” can be construed as having its own meaning, i.e. using half your body’s effort to do something (the ass being a frequent metonym for the body), but that’s not likely the origin of the term.

(As opposed to say, “taking things for granite”, which is purely a result of mishearing and doesn’t have any meaning on its own).

The alternative can be “having your (entire) ass on the line”.

Or, to quote Ron Swanson from Parks and Recreation, “Don’t half-ass two things, whole-ass one thing.”

Loli, your English is fabulous!

This was on another forum if you’re interested.
https://english.stackexchange.com/questions/172341/the-origin-of-the-term-half-assed

I think “half-assed” involves more carelessness than “haphazard.”

“Bone apple tea?” Sounds like “bon appetite.”

Huh! I would have guessed that there was at least a small difference between them, but according to dictionary.com, they’re basically the same:

half-assed: adjective Slang: Vulgar.
1. insufficient or haphazard; not fully planned or developed.
2. incompetent; lacking sufficient ability or knowledge.

When you remember that it’s pronounced hap-hazard and not as ph = f, like haffazard, it seems less likely to me.

Is it not half donkey-half human?

@smudges I’d say half-assed is less specific than haphazard, since haphazard is “lacking any obvious principle of organization” but half-assed can also just mean “insufficient”, not necessarily in terms of organization, but maybe just in terms of effort.

@Zaku Exactly. Which is why I was surprised that they were synonyms.

I would say it is used to describe something done without appropriate care. Haphazard actually implies it was strongly influenced by chance. When I say someone did something half-assed, I mean they did a crappy job, usually due to incompetence or laziness or both.