Dr. Elizabeth Green is a chucklehead.
This was in the same set of aphorisms in which Wilde noted “Nothing compares 2 U.”
Bon jour Found it on the internet, did you? 
QFT.
I don’t disbelieve you. Just wish we could have a cite to prove it. You’re probable right.
I just took it back to a Google book cite from 1959. Business school journal.
I recall seeing it on the Odd Couple, but had heard it before that among military guys, and perhaps even before that in college (1965-67).
I wish whoever said it first had also said it last.
Whenever someone says that, I like to ask, “OK, list all the assumptions you’re making.” The smart ones laugh. The dumb ones say “None!” in which case I get to laugh.
Good assumptions don’t make an ass of anyone. Bad ones do. It’s not always easy to tell between the two, but when we find we’ve made a bad one, it’s a learning opportunity. Not to never assume (which is impossible).
When someone at work mentions an assumption they’re making, I say “Good! Can we test that?” It most often comes up when debugging, and it’s surprising how often really good assumptions turn out to be false. You’d think that after a while, the surprise would fade, but it seems it’s the gift that just keeps on giving.
That one I heard (as “the Siamese National Anthem”, “Oh wa ta na Siam”, to be sung to the tune of “God Save the Queen”) when I was a kid, from another kid. That was in England, in what must have been about 1960, so it definitely long predates The Odd Couple, who merely seem to have bowdlerized it a bit.
As for the “ass - u - me” thing, I do not remember specifically, or otherwise know its origin, but the suggestion of Benny Hill sounds quite plausible to me. He did actually go in for that sort of rather ponderous wordplay sometimes, and it is worth pointing out that his show ran on British TV from 1955, so it was around for a good fifteen years before The Odd Couple debuted on US TV.
Mind you, I imagine Tony Randall managed to make it a lot funnier than Benny ever did (and I say that as a fan and admirer of Benny). The Odd Couple may well have introduced it into America, and, maybe, generally popularized it. Indeed, I doubt if it would have been very funny in the show, despite all Randall’s talents, if it had already been well known in the USA. (Benny Hill, although he had long been well known in Britain, does not seem to have been shown in the USA until much later, the late 1970s.)
Also, I am totally on board with middleman’s rant (although I am baffled as to how “deduce” which means something quite different, almost opposite, can be used as an alternative).
It was Jack Klugman, not Tony Randall, who delivered it on The Odd Couple.
So. . . instead of Oscar Wilde, it was Oscar Madison. . . . Anyway, while it might not be the first occurence of the phrase, I’d submit that “The Odd Couple” was gave the phrase the currency that it has.
If you watch the clip linked in post #42, you’ll see that it was Randall.
I’m another who first heard in on TOC. I’m a pretty big Abbott & Costello fan, and I’ve never heard them do it, though that doesn’t mean they never did.
There was a mediocre sitcom in 1990 called The Fanelli Boys. I remember one episode in which one of the characters pulled the routine on his dumber brother. Later, someone said something to the brother that began with “I presume…” and the brother replied “You presume? You should never presume, because when you presume…” He wrote the word, then stared at it in confusion for a few beats. “When you presume… you press you to me, you ass.”
Well, hell, I was relying on my memory and I just assumed…
When you assert, you make an ass out of the Emergency Response Team.
This smells like a military joke, as told by sergeants.
I would assent, but that would make an ass out of a walking tree.
For Fred Willard, that seems to be pretty unfunny.