be out to lunch

1. Literally, to have left one's desk or job to go eat lunch. Janet is out to lunch right now, but I can give her a message. George is out to lunch? Darn, I really needed to talk to him about this. A: "Hey, where's Alan?" B: "Oh, he's out to lunch with some of the guys from Accounting."

2. slang To be crazy. Don't listen to a word he says, he's out to lunch. You're out to lunch if you think that plan will work. You can't tell people you want to start a business selling bees as pets—they'll think you're totally out to lunch!

3. slang To be oblivious or inattentive and thus behave in silly or strange way. Did I just say that two plus two equals five? Wow, I'm really out to lunch today. I hardly ever get any of my messages because my receptionist is perpetually out to lunch. Dude, are you out to lunch? Quit pulling on that door that's clearly marked "push."