Step One: Steal your friends phone and run into the other room(don't let them know)
Step Two: Go into their contacts and pick someone embarrassing
Step Three: While it's ringing, run to your friend and hand them their phone.
This will cause them to act like an idiot while they try to answer their phone, or if no one answers, while the person calls your friend back and has to explain what happened.
Kellen- phone grenade!
Bill- uh,uh,uh what?