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I'm gearing up for April 1st. Nothing beats filling a car with balloons so that the owner opens the door and has balloons going all over the place 
but have seen the one of the aluminum foil covered office. Definitely time-consuming and funny!
It took time, but oh, was it hilarious. We still laugh about that one 
.
As well as the office "upgrade"!
http://www.boredpanda.com/pranks-april-fools-day/
One that I facilitated was by being the guy that brought tools to school. You know, for taking things apart. Such as removing mirrors from the bathrooms in the Field House (and sometimes removing the plumbing, too.) One of my friends helped me get the mirror off the wall in one piece, and then we kept it in the cabinet for the percussion section.
My other friends in band then took that mirror out on the lawn in front of the Field House during lunch (we had hour-long lunches right after band class) when they went to eat lunch. They also had a straight-sight view of the glass doors to the principals' offices. And since it was a bright, sunny day in the spring, they shone reflected sunlight right through that door, moving it away only when someone walked in or out. We found out later that they'd managed to burn out the a/c unit for their offices!
Now, the only memorable prank I ever pulled was in chemistry class. We had the epitome of the "absent-minded professor" for a teacher. He never really knew what we were doing during lab, even though we had instructions to follow. All too often it was all so easy that we did the experiments quickly and then were goofing off with the equipment, including having cork-wars with test-tubes over the Bunsen burners.
That led me to remember a little bit of physics, and I filled one test-tube with a little water, shoved a cork all the way down the tube until it touched the water, and then left it sideways on the flame-spreader over a still-lit burner (like I said, the guy never checked anything, even for safety!)
Most of us students knew what I'd done and said nothing as we went back to our seats for the rest of class. And then:
POP!
Crash!
"Who's back there?" the teacher asked and rushed back to the lab section as the rest of us tried to hold back our laughter 
I think that's also the class where I got the magnesium strip. I know one of my classmates managed to walk off with a full roll of it (probably at least a pound worth!) I don't think our teacher was there the following year.
were to take the band-leaders batons and pencils and toss them up to the high ceiling, trying to get them stuck. I think we managed to get about a dozen of each stuck in the ceiling 
I love practical jokes that are funny and harmless. That is a good one! 
Fake one hundred dollar bill on a fish line is hours of entertainment.
You can even do it to the same person more than once, so long as there's at least a few months' time between.
You know those little Post-It notes, like 2" x 2"? Put one on the bottom of the mouse, over the light and sensor. Mouse rendered ineffective without actually doing anything to any hardware or software.
People take forever to get it. Some never do 
brilliantly so! 
And I'm not sure how I came up with that one. I know I didn't see it used online. Probably more like being fascinated with how the optical mouse works, and then thinking, "It's interesting how the light and sensor makes this work. If it were interrupted, then it would stop working. Hey, that gives me an idea!"
I can't test it at home (and am not working at the moment) because I don't use a mouse. I suppose if someone hid my stylus...but that's one reason why you buy extras 
Here's one you can try that I just imagined, though I don't know if it'll work (I don't use any wireless peripherals at home.) Switch the keyboard and mouse transmitters between cubicles.
You'd probably have to do it strictly with cubes next to each other, but it should also work where you have four cubes grouped. That way, each cube can affect at least two other cubes at the same time, and so on. Should be fun to be in the area when they're all yelling "WTF is wrong with my computer?" 
before they caught on. It was especially effective to do it on a Monday morning .
Then they're especially vulnerable
You are worse than I thought.
Great idea!
So, you hit them after lunch
of evil. 
Even better idea!
And when we would visit with our dog, sometimes he left a "present" - we always meant to pick it up on our way back home, but you know...
we'd forget
So he went to the hardware store and bought a couple of those little flags that they use to mark gas lines and stuff, so when he came across a "gift" he would put a flag by it so we would clean it up.
One day we went to the hardware store and bought about 20 of those little flags and stuck them all over the yard...giggling the whole time. When he came out to see why we were laughing - he saw a yard full of little pink flags fluttering in the wind - then we told him one was for real and ran away
My brother is an electronics wiz. When we were kids he hooked up a CB handle to the TV. He could talk through the television speaker which terrified me.
He had a ball when The Exorcist aired one evening
absolutely awesome!
I was 'on duty' in a real estate office one Sunday.
Directly across the street was a tavern.
I watched a friend pull in and walk into the bar.
I gave him about five minutes and looked up the number for the bar.
The bartender answered.
"Murphy's."
"Do you see a guy with white hair and a flattop haircut at the bar?"
(This was several years ago.)
"Uh...yeah...?"
"I'm a friend. This is a prank. Would you just say "Frank? A call for you."
He did it!
"Hello?"
"Frank, this is GOD! I'm watching you!"
"WHO IS THIS! WHERE ARE YOU?!"
"You're in there drinking on the Sabbath. I'm watching you."
"Hold it. TROF? Is that you? WHERE ARE YOU? You bastard."
"I'm across the street. Saw you pull into the parking lot."
"Damn. I went fishing this morning and stopped in here for a burger and a beer on the way home. I've never been in this place before. How could ANYONE know I was here? You really had me going."
Frank, this is GOD. 
but you aren't wrong, either!
You are killing me!!!
rofl:
He had an upside-down metal dish pan iced for his wife's birthday cake.
She couldn't cut it.
He had 100 one dollar bills made into a 'notepad' at the local printer's place.
He'd shop around town and peel off three or four of his 'notepad' bills to pay for things.
"Just made these up today."
But freaking evilly perfect
My goodness the stink must have lingered in the air for DAYS!
I think the super gluing the coffee cup is one I need to add to my repertoire!
I am just smirking at the friends and family participating in this thread.
There are far too many ideas to leave around just sitting there .
