The phrase "a complete opposite of" is correct and usable in written English.
It can be used to describe something that is entirely different or contrary to another thing.
Example: "In terms of their beliefs, she is a complete opposite of her brother, who is very conservative."
Alternatives: "the polar opposite of" or "the antithesis of".
But there must be a complete opposite of you around here who will bother Sarah equally, right?
With her long black hair, sweaty skin, and deep dark eyes, wearing black shoes and black garments, she was a rare beauty, a complete opposite of the women I had photographed up to then.
Over the next 20 years of the show being on air, Bart would continue to play pranks on Skinner and Willie often coming out victorious, a complete opposite result of this episode.
Later that year she joined Instagram, a platform dominated by a woman on the complete opposite of the pop-star spectrum, Beyoncé's primary foil in PopStarVille: Rihanna.
Understand that a formal dance is the complete opposite of an informal one.
The second portion of the exhibition operates as a personal dreamworld; in effect, the complete opposite of an impersonal, efficient factory setting.
I can link together a series of anecdotes, which are the complete opposite of a trend.
Once there, however, they are shocked to find themselves in a desolate land, the complete opposite of their expectations.
They chose to send her to a place that was the complete opposite of what she knew, a refuge that reintroduces captive chimps into the wild.
It is cruel irony that the refugees were at a welcoming event, and were treated in the complete opposite of a welcoming manner; but worse irony that they came to Canada seeking refugee from years of war and violence and found themselves victims of a violent attack.
But Rose has another experience that lasts a day and a night and a day, one that's the complete opposite of the hell he suffers at the hands of his torturer, a jaded, perversely loquacious, cheerily nihilistic American agent named Harper.
