(For reasons I've never fully understood, people on almost all SE sites are very adverse to proposing negative answers, such as the one I'm going to propose here. Maybe there's a reason for that, but I figure I'll put it out there...)
I think the real answer to your question is "No, there is no one word to encompass the entire definition you are looking for."
I respect the intention of other answerers, to try to provide something approaching what you are after, but in the end, I think that misses the intent of the question. Any one of the suggested words, used on their own, will ultimately not accomplish what the questioner seeks, which is to use only one word and yet convey the complete meaning. "Spooking" does not contain any element that conveys "for fun". "Prank", "tease", and "practical joke" are not bound in any way to scaring someone, as they can be to simply surprise, embarrass, or cause laughter.
As much as I believe in, and love, the English language's ability to express any concept, that doesn't mean it has a built in word for everything. There are lexical gaps, which mean some things require a little explanation.
To convey what you want to convey, you will have to couch your phrasing in some amount of explanation:
I scared my friend just for fun.
Just for the heck of it I spooked my friend.
On a whim, I pulled a harmless, but scary, prank on my friend.
This isn't a limitation of English, or any language, it's the strength of it. Having a single word for every nuance of every little thing would be a maddening exercise of semantics. Modification through explanation is what lets us convey anything and everything without having to be simply walking definition databases.
Anyway, sorry to soap-box a little in the answer, but I'm a little confused by the hesitancy to not simply state when there is no word for something.
Also, as an aside, a question I'm inclined to ask out of curiosity is, "does any language have a word for that?"