According to the Men’s Health guide to style:

Rule #17: Wear Flip-Flops Only at Home

What makes a man a man? He is strong. He is certain. He is prepared at any moment to meet a manly challenge with courage and fortitude. When a child wanders off the curb into traffic, when a date is hassled by a street tough, when a fire breaks out and someone needs resucing, a man is there, fast and ready. He is not skipping cloppity-clop-clop down the street, squeezing his toes together so his flip-flops don’t fall off.

I couldn’t agree more.