I've still yet to see anyone who's gone far enough to "attempt" to insult me on FG.
I've seen a few people try and communicate with me, though. I've seen a couple "GGs" or "GG" after having some balanced matches in 1v1s (I've taken to using it myself since I first saw it) before my opponent left, and recently I saw someone put in "2LAGGY4ME" after one match and following it up with "CYA!". I certainly wouldn't classify any of that as insulting.
I guess I've just been really fortunate in my time in FG so far. I wouldn't say I've been entirely free of bad matches in online Smash (the first time I ever entered an online battle, I found myself in a Taunt Party that almost immediately ganged up on me before I even did anything) but I've never been called names or personally insulted.
Then you are indeed a lucky one. I've actually been playing For Glory less frequently than I used to cause it's actually starting to become a little tiring to receive salt at every twist and turn. You can only put up with so much for so long after all, and I'm starting to reach the end of my rope. I've actually developed a bit of a toxic mindset now in which I automatically think "Okay, are they gonna throw out an insult now?" if someone manages to win. It's just what I tend to expect out of For Glory these days after so much salt on countless occasions.
Perhaps I'm severely unlucky, because I honestly don't know why I receive so much salt.
I play as

70% of the time on For Glory, so it's not like I'm playing top tier characters or ones people have gotten sick of seeing countless times (Link, Cloud, Ness, etc). I also have a very aggressive play-style and actually, ya know... Adapt when it's needed.
It's honestly not like I'm pro good either. I'm very average, but probably a little above average by For Glory Standards.
It's even doubled, or probably quadrupled in 2V2s when you have an actual friend to play with you. Today we won the first match with a pair, and they went double Link and spammed the whole time. They got a last second kill at the very end and won by a score of +1. So it was 1-1 win wise, yet they decided to say we sucked, called us trash, and even said I "Was a girl", which... Uh, yeah.
I haven't received that kind of insult since the 3rd Grade. I guess For Glory is starting to find less creative ways to spill the salt.
Either way, encountering that kind of stuff each and every time you go into For Glory just wears on you. A lot of us has thick skin, but sometimes those salty players can pierce it if worn down enough. It's kind of upsetting that I can't enjoy For Glory like I used to. Oh well.
Salty players will be salty players I guess. Not much can be done about it really.