I'm extremely uncomfortable in bare feet and hate exposing mine. This includes flip flops, which I refuse to wear. Not to give too much info, but my feet often swell so much on long flights that some of my shoes literally will not fit. On long-hauls, I almost always wear some kind of comfortable slip-on shoe (loafers or slip-on boots), and they come off the minute we leave the ground. However, a clean pair of socks always stays on, and I find this to be extremely comfortable. YMMV, though. If you prefer flip flops, then by all means wear them (as long as your feet are clean and don't stink ).