Change a friend or coworker's tech settings to another language. Get hold of their Facebook, phone or computer and change all the settings to Latin, or Spanish, or German, anything they don't speak.
Change a few common words on Word or Outlook autocorrect. When your friend tries to type something, it automatically puts in the misspelled word. You can also do this in your friend's autocorrect on their phone so when they try to text they get really weird or hilarious words.
Dip the ends of pens in clear nail polish. Do this to your coworkers or your family members. The ink won't be able to get through and no one will be able to write anything.
Put clear nail polish on some soap. Leave it in the shower or by the sink so you can watch. It won't lather and your victim(s) won't be able to wash their hands, or figure out why the soap won't work.
Pretend raisin cookies are chocolate chip cookies. Bring a large batch of raisin cookies into work and say that they are chocolate chip cookies. Watch as everyone gets really mad when they take a bite. To spice it up a little put some pepper in.
Fill a mayo jar with vanilla pudding. Watch as someone makes a sandwich (or be really helpful and make them a sandwich). Or you could grab in down while you're with your friends and starting digging into the mayo.
Switch the salt and the sugar. Put sugar in the salt shaker and put salt in the sugar bowl (or even in the sugar bag).