When your mate says something ill (strange, funny or medically related comment) and you think that it would be a good idea for them to sing that word or phrase really loudly, you shout, SING THAT!! (it has to be said in an ill high pitched voice too). If your mate fails to sing the word or phrase, a common follow up is, SING IT!
Andrew - 'granulomatous inflammation'. Pete - 'SING THAT!' Andrew - 'GRANULOOOMATOUS INFLLLAAMAAATION!' Pete - 'you're ill.'