Wait till everyone settles down and when you feel that everyone’s relaxed dial your number on another phone. Either excuse yourself when you do this so they don’t see you or have the number on speed dial and make the call without taking out your phone from your pocket. Once you hear the fart sound end the call immediately. Don’t let it repeat.
Now sit back and watch your friends as they accuse each other of farting. The more people there are the better because there’s more to blame.