to shock or surprise you.

He has a record of arrests for shoplifting that boggles the mind.

It just boggles my mind how many people think they're the only ones who are having a hard time.

• not be the marrying kind
• not be the only pebble on the beach
• not be up to much
• not be up to scratch
• not be worth a dime
• not be worth a fig
• not be worth a hill of beans
• not be worth the paper it's printed on
• not be worth the paper it's written on
• not be worth the paper they're printed on
• not be worth the paper they're written on
• not be your bag
• not be your brother's keeper
• not break the bank
• not breathe a word
• not budge an inch
• not by a long shot
• not by any stretch
• not by any stretch of the imagination
• not care a fig
• not care a hoot
• not care a toss
• not care tuppence
• notch below
• notch below someone