I got a classic prank I pulled on a couple friends this year.
I had a friend call me the day before April Fool's Day asking me if I could stop by and fix her computer (which they had just got back from a local computer repair shop, by the way). Apparently she was able to get sound from any games/programs/etc she had installed on her machine, yet not from any web sources (such as youtube). I told her I couldn't make it over that day, but I could stop by tomorrow (which would be April Fool's Day; and no, I wasn't already hatching the whole thing at that point; in fact, it didn't dawn on me until I had already been over to her place and fixed the issue, and was gonna tell her it was fixed). But I tell her it should really be the repair shop that fixes it, seeing that they had just given it back to her all 'fixed' not a day before. So she calls me back a few hours later and tries telling me the guy at the repair shop had told her it was because they had XP on there, and all the hardware was optimized for use with Vista (the machine came pre-loaded with Vista Home Premium, but the husband wanted to put XP on it), and the problem could only be fixed by reinstalling Vista back on to it! I immediately told her the guy was full of crap....seeing that the OS knew how to route sounds from locally-installed software yet didn't know how to properly route sounds from the web? C'mon!! Anyway, fast forward........
I get over to her place the next day (April Fool's Day) to find out now NO sound at all is working, and proceed to do all my normal troubleshooting rituals for the issue at hand (verify drivers are up to date, uninstall/reinstall the sound device via device manager, etc etc). Finally determine the cause being the audio cable for the speakers being connected to the wrong port!
So I get it all hooked up right and sound is working again, and go find her to tell her it's all working again. About halfway up the basement stairs, it dawns on me what (holi)day it is, and I hatch up a devious plan (what I failed to mention up to this point is that she thoroughly believed I am/was her own 24/7 tech support contact, and would call me anytime of the day or night (my favorite was one time at 2:30am, when she knew I had to be at school at 7am

) for help).
I find her and let her know (all straight-faced and everything) I've tried anything and everything in my bag of tricks to fix the issue, but could not get it figured out and proceed to tell her that as odd as it even sounds I was beginning to think there was some validity to the whole "You need to put Vista back on there to fix the issue".
Needless to say she completely bought everything I was telling her, and started getting all bent out of shape and angry at her husband (after all, it was his idea to put XP on it in the first place). Then she sits down and puts her head in her hands and starts getting all depressed because they don't have the money to both take the trip down to Florida and get the computer fixed (and here I am standing there keeping the whole ruse going and not cracking up).
So about 10 minutes later, he walks in from work. She doesn't even let him get the door shut before laying into him about the computer. The whole time I'm standing behind her (still maintaining the ruse), nodding my head and agreeing with everything she's telling him. He doesn't believe any of it and says that maybe both of us working together can figure it out. So I follow him down to the room where the comp is and he starts pulling the tower out to mess with the cabling and I'm like "Dude! What are you doing? I already tried all that!" He ignored me and kept doing his thing, and I said "Dude...stop!! If you keep messing with stuff back there, you might mess it up worse than it was before I fixed it and ruin the joke! Ahhh, hell.....I just ruined the joke myself! April ****ing Fools, Dude!"
No sooner did I get that out did I feel someone slug me on my shoulder from the back. I turn around to see his wife. And man, if looks could kill.....I either would have been on the way to ICU or the morgue!
I sooooo had her going, though! I thought about letting her off the hook when she was getting all depressed about the money situation, but I just couldn't let her get away that easily for such a trivial issue.
I got to her so good with it, that when I went back over to hang out a few days later, she had to tell pretty much her entire family (mother, sisters, cousins, aunt, etc) about the whole thing!
I'll tell ya, though.........I haven't had a tech support call from her since!!
Morale of the story: Don't be abusing a friendship and calling a friend for tech support in the middle of the night when he has to be at school early in the morning!! *WEG*