Related Clues:

• Barmy joke, third in cracker
• A crack up leaves one not right in the head
• Demented, with a crack on the head
• Batty, in Mexico
• Giddy-brained
• Smitten to the max
• Engine off the rails
• Engine not all there?
• Not mentally sound, in Seville
• Lady __
• Wildly enthusiastic
• Batty, in Spain
• Pop superstar, for short
• 'Born This Way' singer, familiarly
• Engine — nuts