Can Adults Smack Children?

No wayy! Adults, although they have my respect & everything, they should know that to be respected, you should show respect too, no matter what age.

If an adult "smacks" me, the adult has something coming.

OF COURSE, not if the adult is one of my parents.

Anyone can smack anyone.
But not every such interaction would be legal.
Perhaps the question was intended to be may adults smack children or are Adults legally allowed to smack children.

Depending on where you live, your parents, minders and school teachers may be allowed to smack.
In some countries it is forbidden for even the parents to smack a child.
Even in countries where smacking is allowed, there are generally laws that would punish an adult who injured a child, even if they claimed it was just a smacking.

There is a lot of debate in the world as to whether smacking should be banned completely.
Normally a parent smacking a child is not a sign of disrespect as with any other form of discipline or enforcement of rules, the interest of the parent is benefiting their child, even if the child does not quite see any benefit at the time.