What comes next?
If the kid says anything about being slapped, inform them they are "just butthurt".
Explain to them why they should not be upset.
Help them to understand that your time is precious; and by slapping them you were simply saving your precious time ... which is your birthright, no matter how inconsiderate and intolerable it may appear to others.
Drop the knowledge on them that the slap was simply to show their peers how much you loved all of them. Reaffirm the time situation and how valuable your time is.
Develop an equation to show how your time outweighs their butthurt.
Dismiss any blowback as nothing more than butthurt; and most importantly, never consider the other persons opinion as being valid.
Always remember, you have math on your side!