doolally

Eccentric; insane, mad.

"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."

"When you've got any God's amount of brains," said Frobisher, "you can pretend to be doolally;[…]"

Carried away by enjoyment, excitement, etc.

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.

'I've never had a pet before,' Darkus gazed happily at Baxter [a beetle]. 'Thank you.' / 'That's all right, lad.' Uncle Max threw his hands up in defeat. 'I can hardly say no, when I know Barty would say yes.' / Darkus looked up, surprised. 'He would?' / 'Of course! A handsome hexapod like this? He'd be doolally about it!'