Hodar, you seem to have a wonderful list of pranks... bet you were a hoot when you were a teen!!
My all time favorite was what the girls did back to us, after we paid a late night visit to their bathroom.
They went to McDonalds and got a bunch of straws. Maybe you haven’t noticed, but McDonalds has the white/striped straws that are a wee bit bigger than everyone elses.
They then cut those straws into 2 inch lenths, and boiled them in their hot pots. Once the plastic was soft, they bent them into “L” shapes and let them cool.
Then, they made a late night raid into our bathroom, and installed them at the top of our urinals, so when we flushed, they squirted water out - stratigically aimed, of course.
So, Sunday morning - the first bunch of slightly hung-over students are all wearing their suits, and making the trek to the church; they stop to make a pit-stop .... and viola’
That was perhaps the best prank I’ve ever seen.