doolally

"Will you write me an Essay on Corsets?" / "On what?" I asked incredulously—knowing that he had been a distinguished soldier, and suspecting that he had suddenly developed what the soldiers describe as "a touch of the doolally."]

You are there to entertain. Education is something we like doing. That's not actually the biggest thing on the night, when people are queuing to get in and paying their money. They want to go doolally to their favourite records.