And I question his/hers intelligence.
People do pranks and scare other people for laughs all the time and we don't question their humanity. And suddenly pranking a cat with a cucumber makes you subhuman?
A tennis match is an interaction of equals (if you're at a comparable skill level).
Pranking hardly, since the prankster knows things the other person does not, and even puts elaborate plots and props against his prank target.
And of course some pranksters have whole teams to help them out (e.g. some college prank where 3 persons prank another etc). Or even whole crews, as in TV pranks.
Is Aston Kutcher inhuman for doing Punk'd?
The reason I don't consider it inhuman (inherently I mean, sometimes it can be when overboard) is that while it causes a little stress/surprise etc, it's usually good natured, and don't mean to do actual harm to the target.