Keep calm and tell him your nickname is Roonil Wazlib <- Harry, you genius.
Keep calm and Draco Dormiens Nunquam Titillandus
Keep Calm ‘cause Slytherins do it better
Keep calm and and.. and.. what I was saying?
Keep calm and do the Hippogriff
“How wonderful! Gnome saliva is enormously beneficial!” said Mr Lovegood, seizing Luna’s outstretched finger and examining the bleeding puncture marks. “Luna, my love, if you should feel any burgeoning talent today - perhaps an unexpected urge to sing opera or to declaim in Mermish - do not repress it! You may have been gifted by the Gernumblies!”
Keep calm and keep off the dirigible plums