None. The professional office is not a fraternity. Hazing is inappropriate.

IMO, any prank beyond the most inoffensive and banal are highly inappropriate. For example, you could give a newcomer a funny gift, or sing a silly song at the first meeting. Even then, it's far too easy to cross lines that many "tech bros" don't even realize exist.

Things like deliberately leaving bugs in code is highly unprofessional. Depending on circumstances, the consequences should range from a stern 1-1 with your manager, PIP, or termination with cause.

Why would you prank them at all? They are showing up to do their job, not be your buddy from college.

You have no idea how they will react to your "prank". They could feel rejected and/or humiliated. It could literally make them quit on their first week. Good job wasting the company thousands of dollars for your little prank.

Prank your friends, prank your coworkers who happen to also be your friends if you want. Don't prank strangers when they're already going through the stressful event of starting a new job.

I've been known to to welcome newcomers with the gift of The Most Interesting Reading on Earth(TM, read: industry specs).

People think it's a joke til they get tired of me asking them if they read it 6 months down the line. All the programming knowledge in the world means squat if you don't understand what you're supposed to be doing with it.

Remove the tracking ball from their computer mouse... Oh wait, I'm the wrong century

Wow, looking at some of the comments I had no idea that even proposing to pull a prank would be met with such stern, robotic, "Let's not hurt anyone's feelings" mimicry. Lighten up, geez.