Yellow card will allow you to tap and show referee's yellow or red card on your mobile device full screen. You can set an optional referee's whistle sound and write and set your customized message that is shown on screen.
An app that should always be with you, just for the case.
Send strong, authoritative, non-verbal message to friends at the party, or intrusive persons without excessive words and discussion.
Last but not least, app doesn't require any special permissions and is not intrusive to your privacy.