1) How it looks. We all agree it simply looks amazing and totally sexy. Much has been said about before about this aspect.
2) The sexual attitude of girls who wear thongs: Now what makes thongs very special to me, is the attitude of girls who wear thong. Don't believe a girl who tells you, she wears thongs only due to practical reasons (e.g. to avoid pantylines, etc.). Of course this might be the case in some rare exceptions, and of course on some occasions girls might in fact opt for a thong due to practical reasons. But to become a thong-wearer in the first place, a girl has to be sexually active (in at least some way) and sexually open. Boring girls or girls who are very conservative towards sex usually wouldn't choose to wear thongs - not even on occasions in which they are by no doubt the best choice. They would instead go for ugly nude coloured no-show panties or they just don't care about their horrible granny-panty VPL.
So this means, a girl doesn't choose to wear thongs for no reasons. You simply don't opt for that kind of skimpy underwear, that shows off your butt and body in such a tempting way without any intentions. Girls who decided to wear thongs want (or are at least interested in) to get fucked. A girl who chooses that kind of provocative underwear thinks about sex and getting her pussy filled with some nice and hard cock. Now this doesn't mean she's a slut who is willing to be fucked by just any guy - she could as well just be fantasizing about her crush or about her boyfriends or husbands cock. But it should be clear to this point, that she does have at least some sexual intentions. And I think thats incredible hot. If you see a girl in public, flashing her thong or wearing leggings that show some nice VTL its just like a sign that says: 'Yes, I like to get fucked and I'm craving for your or someone elses cock!"
As I said before, girls who wear thongs don't tend to be too shy or conservative when it comes to sex. They aren't girls who only have sex in missionary position while the light is switched off (cos if she didn't want to show off - she hadn't worn a thong in the first place). Again this doesn't mean, she's a total nympho, but shes almost definetely open for some fun. She probably likes giving blowjobs, that includes swallowing cum or taking a nice load on her face, she also might enjoy taking it doggystyle, dirty talk, getting tied-up, etc. What I want to say is this: If you think of girls who wear thongs, you wouldn't expect them to be closed-minded or boring when it comes to sex - and actually they seldom are. Coming back to what I mentioned earlier, this makes the sighting of a whaletail or something similar even more sexy. Cos you can be pretty sure, a girl who wears thongs loves to get fucked and you can imagine how she looks on her knees with a cock in her mouth, or on all fours, while she's getting her pussy pumped.
Now keeping all that in mind, I think it's incredible sexy and a huge turn-on for me to see (or even just to know), that a girl wears thongs. Sometimes I imagine how those girls go to the store to buy underwear. There are shelves with all kinds of underwear - but she goes for the thongs. The most skimpy undies that show off her butt in the most tempting way - the same kind of underwear strippers are wearing. She opts for this kind of underwear because she wants to be sexy. She wants to be sexy because she likes to tease or to attract Guys in order to get her pussy filled with cock at a later point. I don't claim she's even fully aware of this in the moment she's buying thong underwear. I don't expect girls to actively think about the relation between wearing thongs and the need of getting fucked. But I think the thought of getting fucked is somewhere in her mind when she chooses the thong. The same goes for the situation when a girls stands before her drawer in the morning and has to pick the underwear she'll be wearing on that day. She might either think 'I'm feeling sexy today, so I'm gonna wear a thong' or she might as well not think about anything and just grap a thong - but the fact that she doesn't think about getting fucked in this moment, doesn't mean she didn't when she bought them.
Its because all of this, that thongs are extremely hot. And thats also why I think its very sexy if ordinary, nerdy, girl-next-door kind of type, or very tough and sporty girls like world-class athletes, etc. choose to wear thongs (of course I've got the good-looking ones in mind). Cos if you see the slutty girl wearing a thong it can still be very hot of course - but you'd expected her to wear such kind of underwear, it simply isn't much of a surprise. But if you happen to see the thong of a girl from the categories mentioned above, it is everything but sure that she's a thong-girl. She could just as well only wear panties or bikini briefs. But now that you saw and you know she wears thongs, you also know another thing with a high degree of certainty: She's eager of getting fucked! And she's craving for cock! Simply hot!