The phrase "about to slap" is correct and usable in written English.
It can be used to indicate that someone is on the verge of physically striking another person, often in a context of anger or frustration.
Example: "He was so angry that he looked like he was about to slap his friend for the rude comment."
Alternatives: "on the verge of hitting" or "ready to strike".
When Marie confessed her infidelity and Wozzeck was about to slap her, Ms. Meier's Marie rashly defied him.
The EU is about to slap a travel ban on him and his ministers, like the one imposed against the Zimbabwean government.
"How?" My mother looked as if she were about to slap my grandfather the same way she had slapped me, but instead she answered him.
But some of the worst offenders are the company's highest earners; you should know, because you're the worst offender of all, and you're not about to slap your own wrist.
In other words, Tata's not about to slap the Jaguar emblem on this thing.
Saw Ken Wye, assistant chief executive of the NCB, has the air of a man about to slap a royal flush on the table.
So, while Ari and the tagging team are out-and-about trying to slap a tag onto our big rubbery humpback friends, the visual observing team is hard at work counting the multitude of predators that co-exist within the protected bays and channels of the Gerlache Strait.
To be blunt, it means something to be concerned about, not something to slap a extra coat of blush over.
Congressional aides know a lot about how to slap around their opponents, but because they're always either taking direction from a president or trying to thwart one, they think very little about how to build support for a governing agenda.
Thing One: We Have Always Been At War With Government Spending: The consistent fear of all of our recent stupid federal-budget crises has been that the U.S. economy is about to get slapped by a wave of sudden austerity.
It took me, oh, about five minutes to slap together.
