i have worn a thong bikini before. the beaches i wore them at they were fairly common tho. if you blend into the crowd, and its a appropriate beach, i see nothing wrong with it.
most of the time i opt for something with a bit more coverage. there are lots of semi revealing bikinis that are not thongs that still look sexy and are far more approptiate for more situations... hehe
To be completely honest I find it rather attention seeking. I do not use the "slut" word, but I find wearing a thong bikini very unnecessary. Regular women's bikinis are revealing as it is I don't know why you would want to go out of your way to wear a thong bikini! And additionally I mean really who are you trying to impress at the beach? No one cares and anyone that does look is either A. Going to look once with a glance back then move forward with life or B. Give you probably negative attention (probably from males) which you will dislike. I personally wouldn't feel respected if I had a bunch of horn dogs drooling over me and cat calling.