"completely disapprove" is correct and usable in written English.
You can use it when you want to express a strong level of disapproval for something. Example: I completely disapprove of your behavior last night.
"I completely disapprove of this," Dr. Ekman said, "even though the Supreme Court has cleared it".
But there are other signs that Tehran does not completely disapprove of Mr. Ahmadinejad's behavior.
If you're a parent, your son or daughter will probably fall in love with someone sooner or later - but what if you completely disapprove of their choice?
And nearly the same amount (73%) completely disapprove of the what Trump has done so far in office and how he's gone about it.
Under a binary approach, voters in this category must decide which way to answer, but either answer is not actually true, since they do not really approve, but at the same time do not completely disapprove either.
Nearly half (48%) say they completely approve of the job he's done so far, with 34% saying they approve of what he's done but not how he's done it, and only 14% saying they completely disapprove.
An incredible three-quarters (73%) completely approve of the job he's done so far, while only 1% completely disapproves.
A little less than half (46%) disapprove completely of the job he has done so far, but only about one quarter (27%) completely approve of what Trump has done and how he's done it.
And not all scientists disapprove.
While women with a college degree are more likely to say that Trump is doing worse than they expected (30% vs. 22%) and that they disapprove of the job he's doing completely (46% vs. 38%).
Lewis completely routed the interviewer, who asked him, "Tell me, Lewis, why do you disapprove of the use of four-letter words in literature?" He said, "Because they are not erotic enough!
