I'm not big into practical jokes but it seemed there were a lot going on while at the MTC. I actually did one, which is not my nature but it seemed pretty good at the time. There was an Elder in our district who was deathly afraid of needles and was a nervous wreck leading up to getting our "peanut butter" shot. I don't know how they do shots now but back then you would get a notice in the mail along with all of your district with the set time to go and get them. After my shot I saw a lady filling out the forms that were placed in the mail room advising the missionaries of their appointed shot time. Anyway, when the lady wasn't looking I grabbed one of the slips filled it out and asked someone in the mail room to place it in our district's mail slot. The kid barely made it through his first shot and his face when informed that the lot used for his immunization was expired and that he would need to come in again, was priceless. I literally thought the kid was going to ask to go home. I would love to hear other pranks pulled while at the MTC.