This is obviously just my opinion, and you don't have to agree with my little rant that's about to take place...
First off, flip flops are cute! They're great to wear at the beach, they're great to wear to the pool, but for Christmas sake, do NOT wear them as a form of fashion! And personally, it grosses me out walking in New York and seeing someone in front of me wearing flip flops, then seeing how dirty their feet are--and then knowing how those people go into a restaurant or walk around in their home or even get into bed with those flip flop feet.
I don't know why this is a guy thing, but men wear flip flops when they travel. They wear them on the plane and in the bathrooms and... it's gross. Again, it's just my opinion, and certainly a pet peeve.
I have an obsession when I'm standing in line whether at Starbucks or at the airport where I find myself looking at shoes and feet. Honestly, people's feet are really not the most attractive part of someone's body, and flip flops do nothing to cover up that fact.
So again: beach, pool, for the summer...or keep 'em at home. Simple as that.