I call them flip-flops. I find that calling them 'thongs' usually causes confusion XD
Principal on intercom: Students, remember the dress code! You are not permitted to wear thongs to school. *click*
*80% of students in the school start laughing (which, I must add, is kind of immature)*
Principal on Intercom: *click* We mean the shoes. *click*
...Anyway, I call those shoes without the toes that aren't flip-flops 'sandals' (if you know what I mean). I've never heard anyone use that other name.