One time, in high school, my Drama class was putting on the Night of One Acts theatrical performance, and I was chosen to do a morning announcement about it over the PA system. I ended with "...so come to the Night of One Acts, for a night of entertainment, fun, and full frontal nudity!"
I thought it was a fun joke (probably Monty Python inspired) but when I got back to class, our Drama teacher came to me with a tight smile and whispered through clenched teeth, "Why did you say that??" Mrs Lloyd was the best. I never did another announcement.
And as long as I'm sitting here reminiscing about high school funnies... in my final year, I hatched a plan. We had a sign out front, one of those common ones where you switch up the black letters on white background, you know. I first noted which letters were already in there, and then snuck into the Guidance office where the other letters were stored and got the rest I needed. Then I went to the office and told the secretaries that a letter had fallen down on the sign, and I could take the key out to unlock it and fix it. They thought I was very thoughtful. I took the key to a hardware store and got it copied, and that night (March 31, 1998 to be precise) I went and changed the sign.
One side read "MIKE STEFFLER - STUDENT OF THE YEAR", and the other, "HA HA, APRIL FOOLS!" Then I put a combination lock on the sign to thwart any early morning takedown attempts. My dad was so proud of me, my mom later told me.
They called my three closest friends down to the office, and I shit you not, asked them "who would do this to Mike?"

Sooooo delicious!
A couple of months later, the sign read "FINAL EXAMS", and someone had used a stick or something to push the F and the I together, so it looked like ANAL EXAMS. I was called down to the office and they were like "You have a key, where is it?" I quickly ran and surrendered the copied key, making sure they knew I didn't do that one.

Guess they had worked out that I was the original culprit. Good times!