Select one, multiple or all available sounds.You can either play them instantly or set a delay time and then sleep your phone. After the delay time has passed the selected sounds will play in the background. Your friends will never know where it came from. You can also repeat the sounds up to 10 times just to make it more interesting.
If you think you can create more annoying sounds than this dude, record yourself and play that sound! You can do all this in the settings screen (gearwheel icon).
Suggested prank: select one or more sounds like burp or fart, select delay time in seconds, and set your phone in your pocket while sitting close to your friend or member of your family in a quiet environment (such as a car). The burp or fart sound will play and they will think you are disgusting! But you will have the last laugh. Better yet, install it on their phone and program it to play the sound.