Flip Flops, Flip Flops....Flip Flops.
I had the same debate when doing my Lucy cosplay and I agonized over it. I wouldn't trust the floor and usually when asked for a photo I'll take them off or just take the photo with them on.
For sanitary purposes it's never okay.
Beast from Black Butler Book of Circus [95%]
Ramencon 2016 [All Days]
Daisho-Con 2016 [All Days]
Con-Alt-Delete 2016 [All Days]
Katsucon 2017 [All Days]