http://deadspin.com/sports/what-a-prankster/adam-laroche-kno%20ws-comedy-278768.php
Also from that link, apparently Greg Maddux likes to pee on people.
Begs the question: what're some of the best baseball pranks you've heard of, or have been apart of?
well, i do not know how good this is, and i did not hear of it until many years later:
when i was coaching at McCallum in the mid-70s, i had a very good team. two of my best players were also two of the most mischievous on the team. they were aides for some other coach 5th period, which meant that they were free to go their nearby homes, and they often did. one day, they passed the hour until practice by shooting at sparrows with pellet guns in the back yard of one of their houses. apparently, they were excellent marksmen, and they returned to school with a trash bag full of formerly alive birds. they arrived after most everyone had changed and gone out, and although they were hurrying to keep the coach from yelling at them for being late to practice, they tarried long enough to fill many of their teammates' pants pockets with dead birds. i understand there was quite a commotion after practice, but i did not hear about it until we got together for a reunion about 20 years later.