crazy as a bedbug
(as) crazy as a bedbug
Insane. Often used jocularly. Primarily heard in US. Don't leave me alone with Uncle Stu, he's crazy as a bedbug!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
crazy as a bedbugAMERICAN, INFORMAL
If you describe someone as crazy as a bedbug, you mean that their behaviour is very strange or silly. By now she'd concluded that Peters was crazy as a bedbug. Note: Bedbugs are small wingless insects that live in beds and bedding. They feed by biting people and sucking their blood.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012