drop/lower (your) guard

to stop being careful to avoid danger or difficulty.

Once he knew I wasn't a journalist, he dropped his guard and even let me take a photograph of him.

• with a capital C
• with a capital letter
• with a face like thunder
• with a fine-tooth comb
• with all due respect
• with an eye to
• with an eye to something
• with a straight face
• with a vengeance
• with back against the wall
• with bare hands
• with bated breath
• with bells on
• with both barrels
• with brass knobs on
• with child
• wither on the vine
• with eyes closed
• with eyes open
• with eyes wide open
• with flying colors
• With friends like that, who needs enemies?
• with good reason
• with guns blazing
• with half an eye on