a mile wide and an inch deep

said of a person's knowledge, intelligence or, in some cases, opinion. put another way, you're saying the person knows a lot about everything, but nothing about a given topic.

"That Sarah Palin sure knows foreign policy!"
"She's all talking points. Her knowledge is a mile wide and an inch deep."

by OuLiPo February 27, 2010

a mile wide and an inch deep

Impressive at first but with experience, found to be stupid or unimaginative

"That John Kerry seems to have gravitas."
"He's a mile wide and an inch deep."

by octopod April 10, 2004