Generally, April Fool's pranks tend to be funny only to the person pulling them, usually because they involve the prankster just pulling a dick move and yelling April Fool's at the end of it.
This prank video from H Monteroy is an exception and beautifully executed. So, a student's professor has a rule that any incoming calls during class must be played on speaker -- this is where his rule comes back to bite him in the ass.
A student has her friend call as a representative from a pregnancy clinic announcing her positive pregnancy results. The professor is instantly uncomfortable as she tells him that she plans on keeping the child and naming it... well, that's where the prank kicks in.
April Fool's Day score -- Student: 1, Professor: 0